The Queen of quips: Her Majesty reveals her dry sense of humour joking that a pony is a 'prima donna' in candid documentary 

The Queen has been at the centre of Britain's public life for 63 years but a documentary filmed to mark her 90th birthday has captured the monarch's private side - including her dry sense of humour.

A clip from the ITV special, Our Queen At 90, which airs tonight captures Her Majesty joking about her horses, even branding one of her beloved Fell ponies 'a prima donna' as she feeds her carrots.

She even does an impression of the horse looking haughty - showing a side of her personality that the rest of the world never sees.

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The Queen has showcased her good humour in a remarkable clip that captures her making jokes about her horse in ITV documentary Our Queen at 90

Pointing at her beloved Fell pony the monarch says: 'This is a prima donna this. I don't know if you notice her looking at you as if to say "do I look alright?"'

The Queen points towards black pony and says: 'This is a prima donna this. 

'I don't know if you notice her looking at you as if to say "do I look alright?"'

Pulling a carrot from a bag she continues: 'She is a funny pony.' 

The smiling Queen then feeds the vegetable to her steed who spits it out to which she remarks, 'Oh that's a pity.'

A member of staff accompanying her steps in to see if he'll have more success feeding the pony who once again refuses to eat the peeled carrot.

The Queen laughs, and says: 'See, spits it out again.'

The Queen (pictured here with her groom) also mimics her pony with small hand gestures in the amusing clip 

It is this mischievous spark that most surprised the programme's producer and director Ashley Gething.

He told the Telegraph: 'One thing that took me by surprise was the Queen's sense of humour and it came to the fore on one of the most glittering evenings in the Buckingham Palace calendar.

'The Diplomatic Reception is a yearly gathering of London's Diplomatic community. Eight hundred diplomats descend on the Palace, resplendent in their national dress.

She then proceeds to feed her beloved animal a carrot but has trouble when it chooses to spit it out

Her faithful groom then attempts to feed the horse who again spits it out. 'What a pity' the Queen comments 

'We were filming in the antechamber where the Queen and the Royal Family gather prior to the reception. The Queen turned to the Lord Chamberlain and said: “Do you think if we open the doors there will be anyone there?”'

Of course the doors opened to reveal hundreds of people in their finery. 

The programme aimed to catch the softer side of the Queen, documenting a never-before-seen side of the royal, the Queen off-duty.

And the area where she is seen most relaxed is when discussing her beloved horses. 

'Does it look very likely that we can go riding on Friday?' she asks at the beginning of her working day, clearly looking forward to her own weekend of sorts.

The Queen is also seen complaining about the UK weather as it is set to put off her riding plans 

She continues: 'The weather forecast is appalling. I'm rather a fair weather rider at the moment, I don't like getting cold and wet.' 

The Duchess of Cornwall, one of the many royal family members to be featured in the documentary agrees that horses are one of the biggest joys in the Queen's life.

Camilla says: ‘Horses respond to her. It’s a two-way relationship, they both love each other. She has that wonderful smile which lights up her whole face and you can see the real joy she gets from it.’

Camilla also marvels at the Queen’s stamina as she continues to ride out most weekends.

‘Who else is riding at 90? That’s what’s so incredible,’ says Camilla. 

To make the programme, TV cameras were given access to the Queen’s life for a year, from attending public events to simply relaxing at home. 

The Duchess of Cornwall who features in the documentary, praises the Queen's stamina saying: ‘Who else is riding at 90? That’s what’s so incredible.'

She will celebrate her birthday on April 21 at Windsor Castle, but there are events around the UK until June to mark the occasion – the first time a reigning monarch has turned 90.

Members of the Royal family contribute to the special programme, which will be broadcast tonight on ITV at 8pm.

The Duchess of Cambridge tells during the two-hour programme how Prince George, two, affectionately calls his great-grandmother ‘Gan-Gan’ and reveals that she once gave the Queen a jar of home-made chutney for Christmas.

World leaders congratulating the Queen in the documentary include US President Barack Obama, who describes her as ‘a source of strength and inspiration’