Glen Powell is a professional pretender. As an actor, this can include pretending to fall in love. Enter Sydney Sweeney, with whom he had such a great chemistry on Anyone But You that the boundary between fiction and reality became blurred.

ET was behind the scenes in Australia for the Will Gluck-directed picture, and the 35-year-old actor revealed the right recipe for creating a great rom-com. Yes, a perfect ensemble is one of the essential requirements, but protagonists must complement one another, and Powell learned this early on from his 26-year-old co-star.

“A great rom-com doesn’t survive without great chemistry, and Sydney is the easiest person to have chemistry with,” Powell tells Entertainment Tonight. “I mean, it felt like we’d known each other forever, and I think everyone who’s been on the set knows how much I like chatting to Sydney. We make each other laugh. She’s fantastic, clearly one of the most brilliant actresses we have. This film seemed like a rom-com because Sydney is so easy to pretend to be in love with.”

Anyone But You, which opens in theaters on December 22, is touted as a modernized retelling of Shakespeare’s Much Ado About Nothing, and follows two erstwhile competitors (played by Sweeney and Powell) who loathe one other but must pretend to be a pair until romance blossoms between them.

While filming the project all across Australia, suspicions about a romance between the co-stars began to circulate, which was later exacerbated when Powell’s model-designer girlfriend, Gigi Paris, called it split after three years of dating during Powell and Sweeney’s press tour for the film.