Joe Wicks grew up in a "dysfunctional household" with a dad who was a drug addict.
The 32-year-old fitness coach says his father Gary was always "in and out of rehab" when he was a youngster, but he is now clean and preparing to run the London Marathon next month.
He said: "My dad was a drug addict from a very young age, so he was in and out of rehab when I was a kid.
"He's been through the 12-step programme God knows how many times, but he's clean today, which is the most important thing, and he's doing the London Marathon this year.
"I grew up in a dysfunctional household. I grew up on a council estate, but I still had a roof over my head, we still had food, I went on school trips. I wasn't completely deprived."
While Joe insists his dad's demons weren't the reason he turned to a life of healthy living, he has learnt a lot through his father's "mistakes".
He said: "It made me understand how damaging drugs can be to a family and someone you love, so I learned through his mistakes."
But Joe - who is known as The Body Coach - insists he doesn't have any "resentment" towards his dad's former drug taking because he prefers to look to the future.
He added to Happiful magazine: "I don't live with judgement or resentment, I don't have time for it.
"My mum and dad have gone through therapy for so many years, and I always think, "If you keep looking back, what are you doing today? How are you going to feel good today?"
"I love my mum for raising us, and I love my dad for teaching me what to avoid. I really believe you need to have some challenges in life, because you come out of it, and are better for it."
Joe has been getting stuck into a new challenge of his own of late after becoming a father to daughter Indie, seven months, who he shares with fiancée Rosie Jones, and he is learning new things about parenting all the time.
He said: "One thing I learn is to be patient and know that that baby is just learning about the world.
"They may be crying, they don't know what's going on, just cuddle them and you know just be patient and let them find out where they are and what's going on, they've been in the cuddly womb for so long."