Rylan Clark said he needed to "take time out" following the split from his husband Dan Neal.
The TV presenter's weight dropped to nine stone following a "dodgy year" and he plans to bulk up after hiring a personal trainer.
Speaking on The Hundamental Guide To Life podcast, the 33-year-old said: "I had a bit of a dodgy year last year and I took a little bit of time out."
"And then the next thing I knew, I was like nine stone and I was like 'Oh s**t, this ain't good. I'm six foot four!'"
He added: "So I just got a trainer and was like 'Can you make me look a bit buff?' and he was like 'Yeah'."
The X Factor star opened up about his struggle with his mental health following the collapse of his marriage.
He met his ex husband Dan on series 14 of Big Brother, when he presented Big Brother's Bit On The Side.
Dan asked Rylan to marry him on a romantic getaway to Paris and the pair said "I do" in November 2015.
He said he "didn't know if he could continue to live" following the split.
The Celebrity Big Brother winner confessed that he was hospitalised for "safety reasons" after he refused food.
He told The Observer: "It's really strange talking about this, because I've not even spoken about it to my friends. I just never thought I could get that ill."
"I went down to just over 9st and I'm 6ft 4in. It got bad. Like, very bad. And I didn't think it would get better. I needed help," he said.
The BBC 2 host said there were moments where he "did not know himself at certain points" and was "having thoughts and doing things that made him f***** up."
He added: "I didn't think I'd be here. I didn't think I could continue [to work or to live]. I didn't think I'd actually come back. I was very… gone."
However, the star has bounced back and is putting himself and his health first and has hit the gym and put on four stone.
"I’ve decided to look after myself for a change instead of worrying about everybody else.
"Last year I properly lost myself. I wanted to get me back and make a better version."
He's set to present Strictly Come Dancing : It Takes Two in September.
Speaking of his time on Big Brother, Rylan said: "As much as, you know, you got your Love Islands and... I think we have The Circle as well and stuff like that. They're all great shows but, to me, Big Brother is like the OG. It's the original.
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"Big Brother changed my life. I worked on it for so long and I lived and breathed it, but there was just something about Big Brother that there was no interfering.
'There was no producer saying, "Let's retake this. Let's do this again." From the insider's point of view, that never happens.
"When I really miss Big Brother is this time of the year because January, to me, was always Celebrity Big Brother."
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