During her guest appearance on Watch What Happens Live with Andy Cohen on Thursday, the 37-year-old actress recalled what it was like working with Ledger on the 2005 film Brokeback Mountain. Ledger starred as cowboy Ennis Del Mar (opposite Jake Gyllenhaal as Jack Twist), while Mara played his daughter Alma.
"I was 19, but he was only a few years older than me. Yeah, it was pretty crazy," Mara said. "But he was the sweetest thing. That whole experience was really amazing."
"Even though he was only a couple years older, he really took me under his wing," she continued. "Because I hadn't worked that much [at the time]. So, yeah, it was really special."
Mara added that she originally wasn't scripted to play a much younger version of her character in the film.
"When I auditioned for that, I was auditioning just to play that age because I think my character's 19 at that point, but then [director] Ang Lee decided that he would just use me to play, I think she's 14 or something, earlier on," she shared. "I was like 'This is never going to go work, we're only five years apart or something.' But Heath was so amazing, and he made it work."
Nowadays, Mara plays a parent herself -- in real life! -- with husband Jamie Bell. The lovebirds welcomed their first child together, a baby girl, in May 2019.
ET spoke with Bell just days after the little one's arrival, where he gave an update how he and Mara were doing. Bell also shares a 7-year-old son, Jack, with his ex-wife, Evan Rachel Wood.
"Great! Yeah, I'm in love again," he gushed, before offering some words of wisdom to new parents. "Sleep when they sleep."