TORONTO (AP) — As soon as Eddie Redmayne read the script for “The Aeronauts,” he knew whom his co-star should be: His “Theory of Everything” co-star Felicity Jones.

“I read it . with Felicity in mind and the second I finished it, I called her up and I said, ‘I’ll do this if you do,’” the star said. “And we sort of made that very quick decision. It was a spontaneous thing.”

Jones, who was nominated for an Oscar for her performance in 2014′s “The Theory of Everything,” said reuniting with Redmayne — who won an Oscar for the movie — “felt really natural.”

“But the thing that pushed it was that the parts were so good,” she said. “I mean, if one of us had read it and one part hadn’t been good, it would it would never have worked. But they were both brilliantly written. They were both parts that we were ready to do at that moment. And I think it made it feel more of an adventure coming back together and it made the film feel like it was part of some kind of a narrative in some way, obviously pivoting from ‘Theory of Everything.’”

In the true story, Jones plays pilot Amelia Wren, while Redmayne portrays scientist James Glaisher, who find themselves in an epic fight for survival as they attempt to discover how high they can rise in a hot-air balloon in the 1800s. Redmayne and Jones walked the red carpet Sunday for the film’s world premiere at the Toronto International Film Festival.

Redmayne said their previous connection made it easier to film “The Aeronauts.”

“It’s a weird thing when you start a film because you meet people you don’t know often and then you have to play very closely and intimately with them sort of instantaneously. And this film demanded by its essence, the fact that it’s two people for a portion of the film in this basket, a huge amount of closeness,” he said.

The film opens in the United Kingdom on Nov. 6 before its U.S. release on Dec. 6.