Kristen Bell says her new film with fiance Dax Shepard was like a "love letter".

The Hollywood couple star in the new movie Hit & Run, which Dax also wrote and co-directed.

The actress was very flattered when her partner involved her in his newest project.

"When you saw it on paper, it was even more romantic than it comes across. For me it felt like it was a bit of a love letter," she gushed, before Dax added: "Well what you didn't see in the movie is the descriptions of her.

"Which was just swoonville!" Kristen continued.

Dax is impressed with his comedy film. The actor has joked he had to double check the big screen offering was his own in post-production.

"It wasn't until I was sound mixing. I said to a friend of mine, I don't even trust that I wrote those [funny lines]. Let me look this up. I went back to the script and that was the moment I was like 'These people are saying what I wrote!' It's a cool feeling," he laughed.