Rooney, 35, and Joaquin, 45, are known to keep their private lives out of the spotlight, but the 'Joker' star spoke last year about how they met on the set of 2013 movie 'Her'.
Joaquin was speaking to Vanity Fair magazine, and said he though Rooney "despised" him when they first met, before realising she was just "shy".
The publication wrote in their interview piece: "He believed Mara despised him during the making of 'Her' but later learned she was just shy and actually liked him too."
Joaquin - who also worked with Rooney on 'Mary Magdalene' - admitted the 'Girl With the Dragon Tattoo' actress is the only woman he's ever researched online.
He told the outlet: "She's the only girl I ever looked up on the internet.
"We were just friends, email friends. I'd never done that. Never looked up a girl online."
The 'Walk the Line' actor later admitted he feels "so fortunate" that he's had so many great opportunities and experiences throughout his long career.
He said: "Rooney said to me the other night, 'Do you realise how many great opportunities you've had? These films?'
"I said it's true, I've been so fortunate, so many movies where I was like, I don't know if I'll ever be able to top this experience. The experience of making this movie. It was incredible that I found another one."
