Singer Justin Timberlake has credited his fiancee Jessica Biel with encouraging him to face his fear of sharks during a scuba diving trip in Australia.

The SexyBack hitmaker got cold feet when he spotted a shark circling his boat as he and the actress prepared to jump in, and he nearly pulled out of the dive Down Under.

He tells talk show host Jay Leno, "It's not so much that I'm afraid of sharks, it's just that if I were in the ocean and encountered one I'd probably do the same thing everyone here would do which is flap and scream like a little girl.

"I had never gone scuba diving before I met Jessica and she actually talked me into it. And I said, 'I got one rule. If we are on that boat and I see a shark I'm not going in the water, it's not happening.' When's the last time somebody you didn't know walked into your house and you were OK with that? That's where they live! We're sitting on the boat... the first thing I see is a shark!"

Timberlake forced himself to overcome his nerves in front of Biel, and admits exploring the Great Barrier Reef with her was an unforgettable experience.

He adds, "I just had this moment where I looked at her and was like, 'Ahh, whatever!' And we went in. It was actually really unbelievable."