Frozen star Kristen Bell regrets not cashing in on her YouTube fame after a video of her coming face-to-face with a sloth became an unlikely viral hit.

The actress was promoting her movie Big Miracle and running out of things to talk about when her then-fiance Dax Shepard persuaded her to show the video of her birthday gift from him during an appearance on The Ellen DeGeneres Show.

Bell, who is smitten with sloths, had an emotional meltdown as she came face-to-face with her favorite creature - and it was all caught on film.

She tells Rolling Stone magazine, "I had no idea it would end up being seen by 10 times more people than any project I've done. I look crazy, for sure.

"My one regret is that I didn't figure out how to monetarise it.

"I guess it's my gift to the world of secondhand embarrassment."