Daniel Radcliffe has apparently found love with his co-star in new film Kill Your Darlings.
An insider told The Sun: "They were getting very intimate at the party in a vodka lounge, kissing and with Daniel stroking her leg.
"He's usually not one for casual displays of affection so it obviously meant something."
Daniel - who split from girlfriend Rosie Coker in October after dating her for two years - is thought to have fallen for Erin when they were making the film about the literary heroes of the Beat Generation, but is keeping quiet about their blossoming romance.
A source told People: "They've been dating for a while but have been debating going public."
Daniel, 23, also appeared to dodge the question when asked about the brunette after the party at the Grey Goose Vodka Lounge dinner at the Blue Door in Sundance, talking about how much the entire cast were enjoying being at the festival.
"Erin? Oh, Erin Darke?" he said. "Yeah, the whole cast is here. It's fantastic."
Daniel plays Allen Ginsberg in Kill Your Darlings, which recounts a little-known story of murder involving the poet's circle of friends, including fellow future beat heroes Jack Kerouac ( Jack Huston) and William S Burroughs ( Ben Foster). Erin, who has appeared in films such as We Need To Talk About Kevin and The Longest Week, plays a character called Gwendolyn.