06/09/2008 AT 06:55 PM EDT
says a pair of pajamas she shared with Heath Ledger, who died in January, helps keep her Casanova
costar alive in her heart.
"Heath and I had this amazing night out in Venice with my mother," Miller tells June 7 issue of Britain's Telegraph Magazine
, recalling working on their 2005 movie. "It had been pouring with rain. Heath ran out in the middle of St. Mark's square and we were running around, and I slipped over."
"We all ran back to his [apartment] and he gave me these dry pajamas to get home in," Miller says.
Two years later, Miller had the chance to return the favor to Ledger, who often talked about his trouble getting a good night of sleep.
"When he came over to my house last November, and he was having trouble sleeping, I gave them back, to help him sleep," she says.
To Miller, the PJs became a symbol of her friendship with Ledger. "When he died, I was so sad that I didn't have these stupid pajamas anymore, so his father found them to give to me."
Miller keeps the blue checked sleepwear close, and had them with her in Prague during the filming of her upcoming movie, G.I. Joe
, the magazine reports.