Joaquin Phoenix has asked his yoga instructor to marry him.

The Her star broke the news during an appearance on The Late Show with David Letterman in America on Monday (08Dec14), but stopped short of naming his bride-to-be.

He recalled bonding with the yogi as she attempted to teach him a pose called the harnessing of the hog, explaining, "First we do these breathing exercises and I go, 'I can do this...' and then she says, 'We are going to get in the first position - the harnessing of the hog'.

"Before I can say, 'Who is the hog?' She grabs me - and it's a compromising and vulnerable position - and she gets a strap and puts it around me and she's thrusting against me and I go, 'Oh, no! My back pain!' And she goes, 'No, it's emotional back pain'."

He continued, "This is the crazy part of the story. We started dating, and I think she's the one. I proposed to her and she said yes. If everything works out, I'm getting married... I don't know what that says about me."

Phoenix famously dated actress Liv Tyler in the 1990s, and was most recently linked to 20-year-old DJ Allie Teilz.