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Will Smith

Will Smith gave himself just three weeks to prepare to tick another item off his bucket list and run a half marathon in Cuba.

The Suicide Squad star has detailed his latest test on the fourth episode of his new Facebook Watch show, Will Smith's Bucket List, revealing his recent 13-mile run was his first half marathon.

"As I talk the story out, it doesn't seem like a good idea," the 50 year old explains in the new episode. "It's my snap reaction to say, "Yeah, I could run a half marathon.' Then when I have my quiet moments... I think of all the bucket lists this is the one I'm most concerned about.

"In my deepest honesty with myself I really am not sure if I can run 13 miles."

Smith trained by sprinting up sand dunes and studied ways in which he could control his body temperature.

Unlike his other bucket list items, the half marathon was a chance to take care of his health: "My father died about a year and a half ago and it didn't hit me so much emotionally as it hit me existentially," he says during the latest episode of his show. "It was like, 'Oh s**t, I'm next'.

"In terms of pushing my body, I want to keep my body conditioned and more than anything I want to keep my mind strong. It's like I can do anything, like there is nothing I can't do."

And during the show, the Men in Black star revealed he stayed away from alcohol for over a decade while he was a rising film star.

"I didn't drink for over a decade...," he explains. "I was, like, wildly disciplined, so being in this place in my life, even something as simple as taking my shirt off while I'm out of shape, like, you know this for me now allowing myself to be seen less than optimally is new."

Smith completed the race in two-and-a-half hours.

In previous episodes Will skydived for his 50th birthday, swam cage-free with sharks and tried his hand at stand-up comedy.