Josh Radnor has revealed that Elizabeth Olsen "kept him on his toes" as he brought his new film Liberal Arts to Sundance London.
The second film by the How I Met Your Mother actor, which stars himself, Elizabeth and Zac Efron, had its premiere on the opening night at Robert Redford's UK version of the Sundance Film Festival.
"She's fantastic. When you see the film, you can't imagine anyone else in the role," he said before the premiere at the O2 London.
"When I met Lizzie, it was before Martha Marcy May Marlene had come out so not a lot of people knew who she was at that point. She's a very brilliant and intuitive screen actress. She has the poise and comfort that it takes many actors years to achieve. I'm still learning how to do it myself. She kept me on my toes!"
Josh - who is best recognised for playing Ted Mosby in the E4 comedy - is "proud" to show off his "baby" to British audiences.
"It's great. The people at Sundance have been like my guardian angels - they have really responded to my movies and welcomed me. It's always a thrilling invitation to get," he said.
"This is a particularly small club that they've brought over here so I'm looking forward to showing it for audiences here. I feel like if London has a rich history of loving books, the crowds here could really respond to the movie because the movie is a lot about loving books."