JK Rowling and Emma Watson were among the stars sending video messages to Harry Potter's Evanna Lynch ahead of Monday's Dancing with the Stars final.
The Luna Lovegood star and partner Keo Motsepe reached the final of the US show after scoring perfect 10s in one round of the semi-final last week.
Author JK Rowling said: "Best of luck, Evanna. Hope you win!"
While Emma Watson, who played Hermione, said: "We love you. We are rooting for you. Kill it tonight, girl!"
Tom Felton, who played Slytherin Draco Malfoy, joked: "Despite all of our differences at Hogwarts, I want to wish you all the very best tonight!"
Other messages came from Bonnie Wright (Ginny Weasley), Katie Leung (Cho Chang), James Phelps (George Weasley) and Matthew Lewis (Neville Longbottom).
Evanna became world famous when she beat thousands of other girls to be cast as Lovegood in the Harry Potter film series.
She'll be up against three other celebrities in Monday's final - American model and internet star Alexis Ren, US radio personality Bobby Bones and actor Milo Manhiem.
The final of Dancing with the Stars will be broadcast in the US on ABC at 8pm EST/7pm CST.