When Harry was young, he foolishly and recklessly risked his life to save the life of a girl he saw in trouble e.g. drowning, from being kidnapped.
Things happen, and Harry, at such a young age, is exposed to how vicious a veela can be, though he didn't know what she was at the time. Terrified, he ran off, much to the girl's confusion and sadness.
Years later, Harry comes face to face with the creature of his nightmares at the Quidditch World Cup: veela. The girl was a young, vicious veela.
His friends are confused about his "sudden" phobia and aversion to such beauty that frequently ensnares men.
When the Triwizard delegations arrive , he's remarkably chill. He's even friendly to Fleur on the few occasions they passingly interact, and for some reason she finds something familiar about him... until he learns she's a veela. Then his behavior does a one-eighty and he almost dives out of a window to avoid her.
Some people think he's being racist to her for being a veela or part-veela; others who know him better are utterly baffled, with some thinking he has his "first crush" and doesn't know how to react.
Unfortunately, his bizarre reaction to Fleur has the opposite effect: first she thought he was just bigoted as she saw him avoid her on discovering her heritage.
However, it niggled at her: she knew bigotry, and he was displaying none of the signs she'd encountered before. If anything, she'd say he was phobic of not just her but veela as a whole!
Something... didn't add up. She was determined to find out what.
#1: It was Fleur he saved. She always wanted to thank her hero, and in the years growing up she internally romanticized the image of his being a dashing hero -- finding out it was Harry Potter, of all people? Yeah.
#2: It was someone very important, perhaps even fanon veela royalty like a princess that may or may not be related to Fleur. She feels familiarity because the princess in question grew up sort-of obsessed with "her hero", and the command to find him was pretty much spread out throughout Europe's veela population.
Fleur may have found him, but she needs to be sure before or if she sends word....
Yeah, this has more holes than Swiss Cheese, but I think someone might find this amusing for a yandere veela princess terrifying Harry, her future "fiance".
Welp.