Stepmother Mia Farrow and sister Nancy Sinatra pay tribute to Frank Sinatra Jr. who died suddenly while on tour singing his legendary father's songs 

Mia Farrow and Nancy Sinatra have led the tributes to Frank Sinatra Jr. who died of a heart attack on Wednesday while on tour in Daytona Beach, Florida.

Farrow, 71, posted a picture of Ol' Blue Eyes with his then wife Nancy Barbato and their three children, Nancy, Frank Jr. and Tina, writing, 'Condolences to the Sinatra family. RIP Frankie'.

The Rosemary's Baby star was married to Frank Sinatra for two years in the 1960s, making her stepmother to Frank Jr., even though she is a year younger than him.

His sister Nancy Sinatra, 75, posted the news to her Facebook page writing only, 'Sleep warm, Frankie'.

A family statement said they mourns the untimely passing of their son, brother, father and uncle. No other details were provided.

His world-famous father also died from a heart attack in 1998. He was 82.

The musician and conductor's only son Michael, also posted a heartfelt message to his departed father onto Twitter, writing, 'He was a man who was loved so much despite being so flawed - and that was always a great inspiration for me'.

Sinatra Jr. was kidnapped and held for ransom in Lake Tahoe in 1963, when he was just 19, and had already followed his dad into the music business by then.

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Frank Sinatra Jr., who carried on his famous father's legacy with his own music career, has died at the age of 72 from a suspected heart attack. He is pictured left at a concert in Florida last week and right on a TV show in 1968 

Tributes: Mia Farrow and Nancy Sinatra added their names to the chorus of tributes to Frank Sinatra Jr.

He is pictured with his famed father in Manhattan, New York, in September 1963. Frank Snr also died of a heart attack in 1998 

He performed the National Anthem at a New York Yankees game last year.

He was in Daytona to do a show on Wednesday but died suddenly during the afternoon.

Initially, he only felt lightheaded, but canceled the show on Wednesday as a precaution.

The gossip site reported that he said he was feeling better but then went into cardiac arrest.

Grammy winner Steve Tyrell was one of the first people to pay tribute to Sinatra Jr, writing on Twitter: 'I am overwhelming (sic) saddened by the sudden passing of my dear friend Frank Sinatra Jr.'

Seth McFarlane, the creator of Family Guy, added: 'Frank Sinatra, Jr. was a friend to Family Guy, and a friend to me. I'm saddened at his passing, but grateful to have known him. RIP, Frank.'

In his last interview, he told Daytona Beach's The News-Journal that retirement was a 'dirty' word.

He said: 'I think in my generation, when I came along in the early '60s, the type of music that was in vogue in society in those days had moved on to another kind of music.

Son and ex-wife: Michael Sinatra (seen left in a picture from his Twitter handle) is the son of Frank Sinatra Jr. and he posted a farewell to his father on Wednesday. On the right is Cynthia McMurry-Sinatra, the musician and conductor's ex-wife

Freedom: Cynthia is a noted attorney and married Frank Sinatra Jr. in October 1998 - five months after Frank Sinatra passed away 

'I was trying to sell antiques in a modern appliance store.'

He said when his father's health began to decline in the 1990s, what Sinatra held onto was his love of his audience. 

'That kept him alive,' he told the newspaper.

'That honest to goodness kept him going,' Sinatra Jr. said, 'and I have said my philosophy — I'm a backyard philosopher, I guess — is that the dirtiest word in the English language is 'retirement.' '

Sinatra married only once, in 1998 to attorney Cynthia McMurry-Sinatra. They divorced in 2000.

She made a name for herself when she defended a former Yugoslavian war criminal, Esad Landzo in the late 1990s.

She traveled to the Hague to defend him where he was accused of 'beating to death a 60-year-old prisoner and nailing a metal badge to another prisoner's forehead.'

He was also accused of tying a 'lit fuse around one prisoner's genitalia and forced another to perform oral sex on his own brother.'

She apparently lost the case though, as Landzo was sentenced to 15-years behind bars.

In an interview with the Wall Street Journal, Cynthia said she met Frank Jr. in Las Vegas where he was singing. She said that he gave the arguably flattering nickname, 'The Weapons'.

They wed on her father's farm on October 18, 1998 - which was just five months after Frank Sinatra died.

For the past half century Frank Jr has toured the world as a singer; for the past two decades performing his father's classic songbook in his show Sinatra Sings Sinatra. 

In an interview with the Mail on Sunday last year, he described what it was like living in the shadow of his father.

He said he had woefully few memories growing up of his father. He admitted much of what he learned came from the pages of books, fanzines and, more recently, computer searches. 

His family said in a statement to that Sinatra died unexpectedly Wednesday of a heart attack while on tour in Daytona Beach, Florida. He is picture during a show in Miami on March 11

Frank Jr had been touring around the world for more than half a century. He is seen here in Miami last week. In his last interview with a Florida newspaper he said retirement is the 'dirtiest word in the English language'

Frank Jr sits on his father's lap alongside sister Nancy Jr during a beloved family picture in 1948 

His mother Nancy, Sinatra's childhood sweetheart, supported her husband wholeheartedly while raising three children virtually solo until he left her for the movie star Ava Gardner.

First came daughter Nancy (who would later forge her own successful singing career in the Sixties with hits like These Boots Are Made For Walking), then Frank in 1944, followed by younger sibling Tina.

When Frank was born, his father was away on a movie set. His mother, who Frank Jr still saw every week until he died, posed for publicity shots holding her newborn in her arms alongside a blown-up photo of her absent husband.

'My father in those days was in the fat of his career. As anyone in showbusiness knows, when the phone is ringing you take the work while you can get it,' Frank Jr. later said.

But there was a side to the suave, cocksure performer that Frank hid from the world, a crippling life-long battle with depression that Frank Srenior dubbed the 'Black Dog'.

His son says: 'Like any man, his life was highs and lows. At one point he was riding the crest. He was the biggest star in the world.

'Then in one nine-week period, in 1957, his entire world exploded.

'His movie contract was cancelled, he was released by his agency, the wife he adored divorced him (Ava Gardner) and his TV show was canned. 

Kidnapped and held for ransom when he was 19, Sinatra Jr. had already followed his dad into the music business by then. He is pictured right with his father alongside Dean Martin and his son Dean Paul in 1967

Frank Jr. is pictured alongside his mother Nancy and sister Nancy Jr (date unknown)

'Confucius said: 'The man who knows not pain can never recognise pleasure.'

'In my father's case, his terrible times were amplified many times because of his stature. I remember the 'Black Dog' from the time I could not see over the top of this table.'

When asked if he had any mementoes from his father, he said: 'Yes, I have a pair of cufflinks with his initials on them.'

Frank repeatedly spoke of how his own life was 'immaterial', adding: 'I've never been a success. I have never had a hit movie, a hit television programme, a hit record.

'It would have been good for my personal integrity, my personal dignity to have had something like that.

'I have never made a success in terms of my own right. I have been very good at re-creation. But that is something that pleases me because my father's music is so magnificent.' 

Perhaps the one time his father made his love abundantly clear was when the 19-year-old Frank Jr was kidnapped for four days.

The story became headline news around the world and knocked the assassination of President Kennedy (which happened the month before) off the front pages. 

Sammy Davis Jr and Frank Sinatra Jr in the film 'A Man Called Adam' in 1966

A young Frank Sinatra Jr. (right) is pictured in the arms of his father and sister Nancy Jr in 1948

Frank Sinatra is seen for the first time since the kidnapping of his son, Frank Jr, in 1963

On the evening of December 8, 1963, two drug-addled drifters, Barry Keenan and his friend Joe Amsler, both 23, knocked on the door of Frank Jr's hotel room in Lake Tahoe, California: 'They decided the best way to make a great deal of money in a short space of time was to hold a rich man's kid to ransom,' he recalled.

'They pretended they were delivering a Christmas package but the next thing I knew this guy had a gun in my face.'

He was bundled in the boot of a car and driven to a 'safe' house outside Los Angeles, an eight-hour drive away.

Sinatra Sr immediately offered a $1 million reward, an offer countered by the bumbling kidnappers with a request for $240,000.

Frank Jr says: 'I thought my life was over. I'd been blindfolded and held in a dirty house. I knew they were in contact with Sinatra but had no idea what was going to happen.'

The ordeal lasted four days before the money was handed over (it was dropped in a bin at a petrol station) and Frank Jr was released in the glare of publicity.

The kidnappers were caught days later after boasting of their exploits. 

HOW AMATEUR CRIMINALS TRIED TO GET RICH OFF THE MOST FAMOUS SINGER IN THE WORLD BY KIDNAPPING HIS SON... AND HOW THEY DRASTICALLY  FAILED

Chief FBI agent William G. Simons of Los Angeles (left) and FBI Assistant Director Joseph Casper (also left) show newsmen the ransom money recovered after the kidnapping of Sinatra Jr.

Just days after the assassination of President John F. Kennedy—a group of amateur criminals hoping to get rich engineered one of the most infamous kidnappings in American history.

For several weeks, two 23-year-old former high school classmates - Barry Keenan and Joe Amsler - had been following a 19-year-old singer, Frank Sinatra Jr, from city to city, 

They were waiting to find the right time to make their move. 

The pair decided to strike on the evening of December 8, 1963. Sinatra, Jr was performing at Harrah’s Club Lodge in Lake Tahoe on the border of California and Nevada. 

At around 9 pm he was resting in his dressing room when Keenan knocked on the door. He was pretending to deliver a package to the singer, who was just starting his career.

That is when the chaos unfolded. 

Keenan and Amsler tied up Sinatra’s friend with tape, who was relaxing with the star at the time, and blindfolded their victim.

They then dragged him to a car waiting outside.  

The singer’s friend quickly freed himself and told police his friend has been taken.

Roadblocks were set up, and the kidnappers were actually stopped by police, but they managed to get through.

Agents then met with young Sinatra’s father in Reno and his mother in Bel Air, California. 

The FBI recommended that Sinatra wait for a ransom demand, pay it, and then allow the Bureau to track the money and find the kidnappers.

The following evening, Keenan called a third conspirator, John Irwin, who was to be the ransom contact. 

Irwin called the elder Sinatra and told him to await the kidnappers’ instructions. 

On December 10, he passed along the demand for $240,000 in ransom. Sinatra, Sr. gathered the money and gave it to the FBI, which photographed it all and made the drop per Keenan’s instructions between two school buses in Sepulveda, California during the early morning hours of December 11.

While Keenan and Amsler picked up the money, Irwin had gotten nervous and decided to free the victim. 

Sinatra, Jr. was found in Bel Air after walking a few miles and alerting a security guard.

The youngster described what he knew to FBI agents, but he had barely seen two of the kidnappers and only heard the voice of the third conspirator.

Still the bureau were able to track down the house where he was being kept. In the end, Keenan, Amsler, and Irwin were all convicted after they started to fold on each other. 

(Source: FBI)

The three suspects in the Frank Sinatra Jr. kidnapping are shown in court (left to right) Barry Keenan, 23, Clyde Amsler, 23, and John Irwin, 42. They were all convicted after ratting on each other 

Sinatra Sr, who had negotiated directly with the criminals, was bereft after, midway through a call with the abductors, the payphone he was using ran out of money and he had no more coins.

From that moment on he always carried around a roll of ten-cent coins. When he was buried in 1998 a roll of dimes was placed in his casket.

But the final insult to Frank Jr came during the kidnappers' trial.

The suspects were dubbed 'rank amateurs' by the prosecutor. Their defence lawyer tried to sway the jury by implying the kidnapping was all a stunt to promote Frank Jr's failing musical career.

Lawyer Gladys Root told the hushed courtroom: 'This was a planned contractual agreement between Frank Sinatra and others connected with him… was this the publicity he had been looking for to make the ladies swoon over him like Poppa?'

It was a lie but the mud stuck: 'It definitely affected my career. People didn't trust me. They thought, 'There's no smoke without fire.' It was a life-changing experience. It puts you in touch with yourself.'

Keenan and Amsler were sentenced to 24 years while another accomplice, Irwin – the man who picked up the ransom package – received a 16-year jail term. None of the trio served more than five years in jail.

He smokes a cigarette while at the 53rd Annual Variety Clubs International Convention in 1980 with actress Melissa Sue Anderson

The family - (left to right) Frank Jr, Nancy, Frank and Nancy Jr - enjoy a meal together at the New York nightclub, The Stork Club 

Frank Jr and Nancy Jr (left and right) join their father for an event in 1958