The couple sparked rumours of an impending marriage after Rosie turned up to last night's Golden Globe Awards in LA flaunting a gorgeous ring on her engagement finger.
And now reps have confirmed to E! News it's true!
Rosie, 28, looked sensational in a shimmering gold gown as she supported Jason at the Hollywood awards ceremony, where he was one of the presenters.
They've been dating since 2010 and although they frequently support each other at high profile events, they are usually always very tight-lipped about their relationship.
In an interview with Self magazine last year, Rosie said: "'We're best mates. He makes me laugh every day. I almost feel like I never had a proper boyfriend before! It's more work to put your relationship out there than it is to keep it behind closed doors. But my relationship is not a branch of my brand. It's my private life. Certainly, that's how he feels, too."
She added: "I totally believe in marriage, but being in a happy relationship is much more important to me... [Kids are] something that's more realistic in the near future."
More red carpet looks from the Golden Globes:
Copyright: Rex Shutterstock Jim Smeal