Fewer than three weeks after a huge open casting session for the part of Luna Lovegood, 14-year-old Evanna Lynch has been chosen for the role.
Luna Lovegood, known also as Loony, is a decidedly odd student who befriends Harry in the fifth Potter adventure.
Evanna, who's from near Drogheda in Ireland, was chosen from more than 15,000 other girls at an open casting.
She'll start filming her scenes at Leavesden Studios just outside London later this month.
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Evanna told Newsround that it was a "dream come true" for her to get this role.
All about Evanna
She's a HUGE Potter fan
She's got two cats called Luna and Crookshanks!!
She persuaded her parents to take her out of hospital for a day so she could queue up for a copy of Order of the Phoenix!
She has a signed copy of the fifth Potter book
Her dad flew over to London with her for the Luna casting
She added: "I've been a Harry Potter fan for years and years."
Everyone at Evanna's school was excited for her. Tara Gufferty, head girl said: "Obviously the school is on an absolute high since this morning when we all found out.
"It's a fantastic acheivement for Evanna. It's every girl's dream to be working with stars like Daniel Radcliffe."
Other casting announced by Warner Bros. includes Natalia Tena, who's been in BBC drama Casualty, as Tonks.
Imelda Staunton will play new Defence Against the Dark Arts teacher Professor Umbridge.
Staunton recently appeared in the children's film Nanny McPhee.
The part of Bellatrix Lestrange, an evil follower of Lord Voldemort, has gone to Helen McCrory.
She's appeared in the movie of the Count of Monte Cristo.
And actress Kathryn Hunter will be playing Mrs Figg.
Earlier this week, CBBC Newsround revealed that George Harris will play Dark Wizard Catcher Kingsley Shacklebolt.
Filming is about to start on Harry Potter and the Order of the Phoenix.
It will be in cinemas in 2007.