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LeBron James, Bill Hader and director Judd Apatow on the set of "Trainwreck."

(AP)

CLEVELAND, Ohio - "Trainwreck," the comedy starring Amy Schumer, Bill Hader, Tilda Swinton and LeBron James, debuted at SXSW over the weekend. The movie is already earning rave reviews, especially for James' performance.

Amy Schumer and Bill Hader star in "Trainwreck."

When word of the film's existence spread late last year, it was thought James would be a glorified cameo. It turns out the basketball star is a major part of the ensemble.

"It's not just a cameo," director Judd Apatow told USA Today. "He's actually a large part of the movie."

A work-in-progress version of "Trainwreck" premiered to a sold out crowd at SXSW on Sunday. USA Today film critic Mike Snider calls James' performance "revelatory."

In an interview with Entertainment Weekly, Schumer, who wrote the film, and Apatow talked about James' presence on set, which drew other celebrities like Chris Rock.

"Chris Rock was pitching jokes for LeBron, all of which are in the movie, all of which killed," Apatow told EW. "There is a run where he says, 'You have to be careful because you don't want a baby mama,' and he goes on this run about how you handle your baby mama because before you know it, you have to buy her a pantsuit line."

The Daily Beast calls James' work "stellar," while Cinema Blend says James is the "Trainwreck's" "secret weapon." Huffington Post even went as far as to label James a movie star.

The general public will have to wait until July 17, when the film opens, to see James' performance. Let the anticipation begin.