Tom Felton, who plays villain Draco Malfoy turned up sporting his trademark platinum hair, Evanna Lynch aka Luna Lovegood attended and Katie Leung, known for her role as Harry's love interest Cho, was also present.
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Birthday girl: Emma doesn't look like she's had much fun as she arrives home
In fact, the only two people noticeably absent at the celebration in London restaurant Automat, were Emma's onscreen best friends Daniel Radcliffe and Rupert Grint.
Perhaps the no-show of the pair, who play Harry Potter and Ron Weasley in the series of blockbuster films, is the reason why the birthday girl looked miserable as she arrived home at 4:30am on Sunday.
However, the chances are she won't be moping for too long if her mountain of presents are anything to go by.
Tom Felton aka Draco Malfoy is instantly recognisable with his platinum mop and Katie Leung who plays love interest Cho dresses down for the dinner
Emma accumulated so many gifts as the night went on, her dad was weighed down by boxes and bags as he ferried them from the restaurant to the actress's Oxfordshire home.
Unsurprisingly the teenager, who plays the role of Hermoine in the adaptations of JK Rowling's books, looked immaculate at her coming-of-age dinner in a strapless black minidress.
Cry if I want to: Emma Watson can't stay out late because of her Harry Potter contract
Annoyingly, Emma, who has a good behaviour clause in her contract with Warner Brothers, wasn't even allowed to go to the MySpace Beyond The Rave party last week which she was due to attend with her financier boyfriend Jay Barrymore.
"Jay was there on his own," I'm informed.
"Emma wasn't happy to be told she wasn't allowed out." Nor will she be happy to hear that Jay was having a long chat with Tamsin Egerton and Tallulah Riley from the St Trinian's movie.
But there is a little silver lining to go with her cloud.
After turning 18 last week Emma access to her £10.5 million fortune for the first time
She only got her hands on the money after agreeing to enrol on a crash course on being a multi-millionaire, Mail Online has learned.
And, after amassing the huge sum over eight years starring as Hermione Granger, she is reportedly being paid £2.5million for the latest Harry Potter adventure.
However it has emerged that she will have a battle on her hands if she wants to try and blow her millions all at once.
Emma will only have access to her money through a wall of men in suits at Coutts - the bank favoured by the Royal family - which also managed co-star Daniel Radcliffe's estimated £24million fortune.
She has also had to complete a crash course in being rich, given by the bank at the request of her parents.
The actress had to sit through three days of tutorials with other Harry Potter child stars including Tom Felton who played Draco Malfoy in the movie franchise.