"He's really, really nice. A really enthusiastic guy who's really into acting. He's really passionate," Rafe said.
Rafe stars in the Nick Payne play Constellations alongside Happy Go Lucky actress Sally Hawkins.
"She thought it was going to be Ralph Fiennes. You should have seen her face on the first day. She was gutted," he joked.
Rafe, the son of veteran star Timothy Spall, said mixing film and theatre roles was important to him.
"You want to be an actor because you start doing school plays when you're young and that's your first point of entrance into being an actor. I did Calamity Jane and that was what really wet my whistle," he added.
"I think when you do a play you really remember how good you are because not only is it very technically difficult, it's also really scary being up there in front of all those people and trying to remember loads of lines."
:: Constellations opens in the Duke Of York's Theatre on November 9.