Who knows what happened on May 8, 1945 when Princess Elizabeth, the future Queen, and sister Princess Margaret went on to the streets of London to celebrate Victory in Europe (VE) Day. I doubt events unfolded quite as director Julian Jarrold portrays in this lighthearted, rather charming film, but it certainly conveys the genuine feel of the dawning of a new era.
It's hard to imagine an unrecognisable royal - especially one who is heir to the throne - so accepting the princesses had been "cloistered like nuns" for six years and were unrecognisable, is the first hurdle to overcome with this coming-of-age story.
Princess Elizabeth (Gadon) convinces her father to let the sisters experience some rare freedom by claiming she'll be able to tell him what people really think of his VE Day speech.
As you'd expect from a British period piece, humour as well as class are pillars of the story, with the distance between the royal family and their people highlighted in a scene when Elizabeth stands outside the gate of Buckingham Palace watching her parents wave to the crowd.
Social structures are also expressed through Elizabeth's relationship with Jack, a young republican airman (Jack Reynor), who she recruits to help her around London.
As they travel from the Ritz to Trafalgar Square, Soho to the Chelsea Barracks, and everywhere in between, every slice of London's society is celebrating the same thing, but in different ways and with different expectations.
Julian Jarrold (Kinky Boots) does a handsome job of bringing London to life in a chaotic, party-fuelled manner, especially with a large-scale scene in Trafalgar Square.
But the constant drunk celebration becomes wearisome, as you'd imagine Elizabeth's night to really have been, chasing her ditzy younger sister around London.
Princess Elizabeth is far too dignified to get mad at her little sister, and Canadian actress Sarah Gadon (A Dangerous Method) does a wonderful job of portraying the princess. The heart of this fish-out-of-water story, she's the one person who visibly changed from her night out.
Princess Margaret, on the other hand - played delightfully by Bel Powley - gets to have all the fun and provide most of the laughs, but at the sacrifice of any character development.
Emily Watson and Rupert Everett do an excellent job adding subtle humour to their roles as Queen Elizabeth and King George, and you can't help but wish there was a little more for them to do here.
That A Royal Night Out is timed to be released around VE Day's 70th Anniversary and was screened to media on Mother's Day, gives you an idea of the audience who might enjoy this light, frothy, and ever-so-British fun.
Cast: Sarah Gadon, Jack Reynor and Bel Powley
Director: Julian Jarrold
Running Time: 115 mins
Rating: M (Adult themes)
Verdict: As bubbly as the champagne that flows throughout.