HOLLYWOOD — It was months between Jessie Cave's first open-call audition and finding out that she had nabbed the part of Lavender Brown, Hermione's roommate-turned- romantic competition in the upcoming film "Harry Potter and the Half-Blood Prince."

"It was quite surreal," the 22-year-old Londoner said in an interview. "Throughout the process I never thought I had the part, the chances were so slim."

Well, not so slim: Cave appeared in the CBBC drama "Summerhill" and is currently on the West End stage in a critically acclaimed revival of Tom Stoppard's "Arcadia."

While waiting to see the finished film herself, Cave talked about Rupert Grint, who plays Lavender's sweetheart Ron.

The movie opens in Honolulu at midnight Tuesday. (Reviews will be posted next week.)

Do you remember what your first day on set was like?

It's funny, I was filming for six months, but I remember my third day was the big kissing scene. I remember thinking, "Why are they doing this so early?" It helped, actually, because the nerves kind of added to the scene.

If I remember correctly, Lavender's the aggressor in the relationship, right?

Ha! Yes, she is incredibly dominating of Ron. She just wants to be around him all the time, and she's the one who initiates everything. She's one of those girls that's very pretty and very obvious, she's just not really aware of how she's being perceived by anyone else.

How is Lavender introduced?

She's in the Weasleys' Wizard Wheezes shop, and she's kind of ogling Ron. She's been going to school with them for years, but it's not that she's making her interests known.

Were you already a "Harry Potter" fan when you auditioned for the part?

Oh, yes! I'm one of five in my family, and we've all gone through the books at different paces. I read "Half-Blood Prince" before I knew anything about the auditions. So to have already read the character was so great. Also, my little brothers and sisters are so excited and proud.

Did any of them get to go with you to the set?

I brought them all on set, but my little sister, she's 11, she was the one who was in awe of everything. Jim Broadbent was there, and Daniel Radcliffe. I brought her into the Potions classroom and I signaled Daniel to wave at her without her seeing. And then Daniel waved and she thought he had done that for no reason and she was in seventh heaven. She was absolutely star-struck. She almost fainted when she saw Emma (Watson) in the corridor. It is so bizarre to actually meet them, because, you know, they're on posters everywhere.

What's been the best perk that comes with being in a "Harry Potter" movie?

Just to be there every day was so brilliant. I'm so happy with it. I had a few scenes with Michael Gambon, and in the hospital scene, I met all of British acting royalty. I was so scared I didn't really speak. To be in the room with them is quite overwhelming. Someone behind me said, "You're standing next to three Oscars and a BAFTA," or something. Yeah, that made it much easier for me. (Laughs). That was the best thing.