But shortly afterwards the teenager's poise evaporated as her dress fell apart during the National Movie Awards ceremony.
The 18 year-old was due to present the Best Family Film gong at the event held at the Royal Festival Hall when she suffered a dramatic wardrobe malfunction.
Wardrobe malfunction: Emma Watson's Chanel dress came undone as she took to the stage at London's Royal Festival Hall last night
As she stepped on stage to announce the winner the back of her Grecian-style Alexander McQueen gown fell open.
The young actress was swiftly surrounded by flailing helpers who tried unsuccessfully to re-fasten the cream floor-length dress.
Miss Watson was forced to announce the award, to winning animated film WALL-E, while her dress gaped.
One of the stars: Glamorous Emma arrives at the London awards
Even host James Nesbitt attempted unsuccessfully to preserve her modesty.
The starlet took her misfortune in good humour - rolling her eyes at the audience and gesturing at her parents who watched helplessly from their seats.
An audience member said: 'The whole back of her dress fell open and they had to get several lackeys to try and do it up. It wasn't televised as it was during the trailers but the gown was gaping open at the back as she gamely carried on.
'Unfortunately the men who tried to help her couldn't do it up and even James Nesbitt tried to get involved. However by the time she sat down again she seemed to have been pinned back together.'
Cover up: After leaving the awards Emma slipped on a friend's oversized black blazer to head to the official after party
Later that evening at the afterparty at Claridges hotel James Nesbitt commented: 'Yes she had a bit of a problem with her dress but she was very professional about it, you could hardly tell. I tried to help her do it back up but I wasn't much help - it's been a long time since I did anything like that.'
Meanwhile attempts to mend Harry Potter star's outfit after the awards were also unsuccessful.
Instead of attending the party at Claridges Miss Watson went straight upstairs to a suite in the hotel to try and fasten the ensemble.
From glam to grunge: Emma started the night in glamorous white, but changed into a fashionable pair of shorts and long cardigan to join her friends
But after several failed attempts to secure it she abandoned her designer attire.
Left with limited wardrobe choices she opted for something more comfortable and headed to Mayfair club Mahiki to join friends dressed in a mismatched ensemble of plaid shorts and oversized cardigan.
To rule out any further sartorial disasters Miss Watson also opted to change her skyscraper heels for more sensible footwear.
Instead of the handmade Alexander McQueen shoes, made specially for the awards, she danced the night away in flat moccasin style boots.
The actress has just returned from travelling in Kenya and Hong Kong after celebrating getting three straight A's at A Level this summer.
Quick change: Emma slipped into comfortable boots and casual clothes to go clubbing after the party
Level-headed Emma has grown up in the public eye since landing the part of Hermione Granger in the film version of JK Rowling's hit wizarding books.
But instead of letting the fame, and the millions, go to her head the child star continued to live a normal life.
Amongst her work commitments and the glamorous parties she has worked hard at her studies, and could soon be off to Cambridge after scoring straight As in geography, history of art and English literature A-levels last month.
Hard working Emma's down-to-earth lifestyle is all the more astonishing considering her 10.5million fortune, which she took control of on her 18th birthday.
For the current sixth film she is being paid 2.5million, according to an industry insider. And in a particularly canny bit of negotiating her future earnings for the final film will be further boosted by 3million.
However, at her parent's request, Emma agreed to only access her money after taking part in a crash course in how to be a responsible multi-millionaire at Royal bank Coutts.
Emma Watson, 19, was the victim of a gust of wind that caused her a slight wardrobe malfunction at the premiere of "Harry Potter and the Half-Blood Prince". See what Emma has to say about the panty flash on David Letterman in video below.
While on the red carpet at the premier of "Harry Potter and the Half-Blood Prince" in London, Emma's split dress was victim to the wind and showed her underwear.
Emma Watson told David Letterman that it could have been much worse.
The blushing Emma told Dave that this was "a small wardrobe malfunction that happens."
"At least I'm wearing underwear," she added, before hanging her head in her hands to say she's "still learning" this stuff.
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