New mother Rachel Bilson shows off slim post-pregnancy figure as she takes a trip down memory lane at The Unauthorized OC Musical

She's been enjoying motherhood since welcoming her daughter last October. 

However, Rachel Bilson took a trip down memory lane on Sunday night as she headed for a girl's night out in Hollywood. 

And where better for the actress to rock up than at a one-off performance of The Unauthorized O.C. Musical at the Ricardo Montalban Theatre. 

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New mum: Rachel Bilson took a trip down memory lane on Sunday night as she headed for a girl's night out in Hollywood

New mum: Rachel Bilson took a trip down memory lane on Sunday night as she headed for a girl's night out in Hollywood

The 33-year-old found fame playing Summer Roberts in the prime-time drama series set in Orange County, California. 

And she looked to have enjoyed the stage version, which stars singer/song-writer Betty Who, as she left the theater grinning from ear to hear with her gal pal. 

The star and her friend were pretty much matching in the classic combination of white tops and blue jeans which showed off Rachel's slim post-pregnancy frame. 

Stunning: The 33-year-old actress and her friend were pretty much matching in the classic combination of white tops and blue jeans which showed off Rachel's slim post-pregnancy frame

Stunning: The 33-year-old actress and her friend were pretty much matching in the classic combination of white tops and blue jeans which showed off Rachel's slim post-pregnancy frame

Rachel let her enviable glossy tresses do the talking, as they framed her lightly made-up features. 

Earlier in the day the star had attended a baby shower with her best friend - posting an instagram shot captioned: 'shenanigans. #bestfriendsbabyshower @obliviaallen @missleagrace' 

She left baby daughter Briar Rose in the capable hands of her father - Rachel's boyfriend of 8 years - Hayden Christensen. 

Fun: The O.C. actress rocked up with her friend to a one-off performance of The Unauthorized O.C. Musical at the Ricardo Montalban Theatre

Fun: The O.C. actress rocked up with her friend to a one-off performance of The Unauthorized O.C. Musical at the Ricardo Montalban Theatre

According to US Weekly the actor tells Hallmark Channel’s Home & Family on Monday that his treasured little girl is definitely their little princess - as she's named after the original Sleeping Beauty. 

Sounding absolutely smitten with fatherhood, the Star Wars actor told the show's hosts: 'There’s a Disney reference there I suppose. The original Sleeping Beauty is called Briar Rose. Rachel — we both love Disney — but Rachel especially was very keen on the name'. 

The notoriously private couple took ten months to offer the first glimpse of their daughter in a sweet Instagram post Rachel shared earlier this month.

Well-groomed: Rachel let her enviable glossy tresses do the talking, as they framed her lightly made-up features

Well-groomed: Rachel let her enviable glossy tresses do the talking, as they framed her lightly made-up features

The show: Rachel, who played Summer Roberts in the O.C. TV series, watched the stage version, which stars singer/song-writer Betty Who

The show: Rachel, who played Summer Roberts in the O.C. TV series, watched the stage version, which stars singer/song-writer Betty Who

Busy day: Earlier on Sunday the star attended a baby shower with her best friend - posting an instagram shot captioned: 'shenanigans. #bestfriendsbabyshower @obliviaallen @missleagrace'

Busy day: Earlier on Sunday the star attended a baby shower with her best friend - posting an instagram shot captioned: 'shenanigans. #bestfriendsbabyshower @obliviaallen @missleagrace'

Glimpse: Rachel and boyfriend Hayden Christensen took ten months to share an image of their daughter Briar Rose eaelier this month - even then shielding her face from the camera

Glimpse: Rachel and boyfriend Hayden Christensen took ten months to share an image of their daughter Briar Rose eaelier this month - even then shielding her face from the camera

The couple chose to conceal their tot's face in the snap, in the adorable image which shows the first-time parents enjoying some quality time with her in the park.

Shielding her face from the sun, Briar Rose donned an enchanting floral sun hat on her head, which was teamed with a blue and white printed romper.

Rachel and Hayden began dating in 2007 after meeting on the set of Jumper, with the Star Wars Episode II actor proposing just a year later.

The couple called off their engagement in 2010 - though rekindled their romance just a few months later.

Couple: Rachel and Hayden began dating in 2007 after meeting on the set of Jumper and welcomed Briar Rose last October

Couple: Rachel and Hayden began dating in 2007 after meeting on the set of Jumper and welcomed Briar Rose last October

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