Star Trek icon William Shatner has conquered his fear of sharks for a U.S. TV special.

The veteran actor was tapped to feature in Expedition Unknown: Shark Trek for the Discovery Channel's Shark Week event, and spent a week in the Bahamas coming up close and personal with the big fish with host Josh Gates.

Shatner, who turned 90 in March, was "turning white with fear" when he first received the offer to join Gates on the dive, but he was determined to step up to the challenge and face the sharks underwater.

However, guides soon told him that simply getting in and out of the water would pose the greatest threat to his safety, because of sharks surrounding the boat.

"Never mind how dangerous it is down below, getting into the water is the real danger, and getting out," he told U.S. breakfast show Today. "I mean, you have your rump exposed coming out. You get bit by shark..., how do you make that excuse? 'What's that scar on your rear? Oh, it's a shark bite (sic)!'"

Despite Shatner's initial reservations, Gates called the star an "inspiration", adding: "The fact that he's 90 is impossible. I thought, 'Ninety years old? Is he really gonna be able to go diving, and get in with the sharks...?' He was up for everything... I cannot understand it."

Shatner said his age was part of his drive to complete the daring feat, adding "I wasn't sure if I'd see 91. This was the adventure of a lifetime."

Expedition Unknown: Shark Trek premiered on Monday night.