John Travolta works out at 3am for the benefit of his children.
The 60-year-old Hollywood star was recently pictured in a gym in the early hours of the morning and has revealed he's determined to stay in good shape so he can raise his kids.
The 'Grease' actor - who has a daughter, Ella Bleu, and a son, Benjamin, with his wife Kelly Preston - explained: "[I work out] for my health... as you get older, if you have kids that are young - I mean, my son's four and my daughter's 14. I should be really a grandfather, but I'm a father.
"They still want me to play with them at the level of a much younger man. So in order to stay healthy for them, that's what I do."
John - whose third child Jett died in 2009 - also revealed his exercise regime is not confined to the gym.
He said: "I play tennis every day and I lift weights, and I take vitamins and try to keep my health so I can stick around for them."
Recently, it was announced that John is to play O.J. Simpson's attorney, Robert Shapiro, in 'American Crime Story' and he's looking forward to the task.
He told Access Hollywood: "I took a while to decide, but all my friends, all the people I respect most in the industry, said I should take that leap to do something special on television, and I'm doing it."
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