Julia Roberts (left) and Lily Collins
For Lily Collins
, starring opposite Julia Roberts
in the as-yet untitled Snow White movie was intimidating in more ways than one.
"She gave me goosebumps," Collins, the 22-year-old who plays Snow White, tells PEOPLE. "She played the Evil Queen brilliantly. You forget that's really Julia because she's so good. Off camera, she's so down to earth and so sweet. We'd be shooting and she's being extremely horrible to me [in character] and once they yell cut, the first thing she says to me, 'Are you okay? I'm sorry, I hate being mean to you.' "
Adds director Tarsem Singh: "Julia was completely right in saying like, 'I feel so strange being mean to her, because it feels like I'm being mean to Bambi.' "
As for his Snow White: "Lily looks so young – Liz Taylor meets Audrey Hepburn."
The movie is scheduled for release next March. For her part, Collins adored acting with Roberts, 43.
"She's someone that I've looked up to forever, and to be able to be in a scene with her and watch her work is such an honor," Collins said, calling playing Snow White an "incredible experience." "She's so funny and she really brings an energy to the set unlike anything I've seen."
Frequent visits from Roberts's children
– twins Hazel and Finn, 6, and Henry, 4 – added a bit of frivolity to the set, Collins said.
"They were so sweet and well-behaved," Collins said. "Her daughter would sometimes go under her dress and come out the other side. The dresses were so big that she would hide underneath it."
Though Kristen Stewart
is starring as Snow White opposite Charlize Theron
in Snow White and the Huntsman
, scheduled to be released June 2012, Collins said the two projects have differing takes on the classic fairytale.
"I'm really excited for Kristen's version and I'm really excited about ours," Collins said. "[Singh's film] really made the fairy-tale story that we love come to life. There's a bit of everything in it. There's romance, lots of action and it's fun and it's a comedic adventure, too. There are some dark moments, but really it is the fairy-tale story that's been updated and modernized."