Sussex-based television presenter Davina McCall has described how her arduous fundraising exploits last month left her in a "very dark mental place".
The 46-year-old, who was the face of Channel 4's Big Brother coverage for a decade, suffered an emotional meltdown during her charity exploits for BT Sport Relief Challenge: Davina - Beyond Breaking Point.
The mother-of-three embarked on a week-long 500-mile run, cycle and swim from Edinburgh to London, raising more than £750,000 for good causes and shedding plenty of tears along the way.
At one point, television viewers saw McCall, who lives in East Sussex, being pulled out of the water as she completed a 1.5-mile swim across Lake Windermere.
In an interview with the Guardian's Weekend magazine, McCall said the sheer physical exertion resulted in her "sobbing my guts out".
She said: "It was like somebody had opened the floodgates and I let out every single bit of grief that I had.
"I kept crying every day... I think I was just so tired that I had no defences, and I was just sobbing at everything."
She added: "I'm normally a chipper person. If you're in a positive state of mind you can cope with pain and jolly yourself along, but I had moments when I went into a very dark mental place."
The former heroin addict admitted she doubted herself throughout the challenge, but persevered after seeing the work her charity ordeal would help fund at a Sport Relief project in Africa before setting off.
She also said the memory of her half-sister, Caroline, kept her going. Caroline died in 2012 after being diagnosed with cancer.
McCall, who also spoke frankly about her difficult relationship with her mother, said: "She (Caroline) was our other half, she was my husband's sister, and it was the hugest loss of my life. I felt like she was with me (on the challenge) a lot."
Sport Relief is due to take part next weekend. For more information or to donate, visit www.sportrelief.com.