Soap star Beverley Callard was forced to leave ITV reality show I'm A Celebrity... South Africa after collapsing in the jungle camp, before she was diagnosed with cancer.
The actress, best known for playing Liz McDonald in Coronation Street, revealed in February that she has breast cancer.
On Tuesday's episode, filmed in September before her diagnosis, Callard broke down in tears after announcing she would have to leave the jungle, saying she was "absolutely gutted".
In an Instagram video posted on Tuesday, Callard explained she passed out after feeling unwell. "Of course, I didn't know then that I had cancer, but I just knew that it was the last couple of days there that I hadn't felt very well," she said.
The Two Pints of Lager and a Packet of Crisps actress, 69, said: "I went into the Bush Telegraph [the show's video diary room] and apparently I lost consciousness for a little while. I just wasn't feeling myself.
"They took me to a medical hut, and they were amazing, they really looked after me and they said, 'You can't go back'.
"I said, 'Don't send me home, I'm sure I'll be fine'. I've jumped out of a plane, I've hung off a cliff, and I did want to succeed and make it through to the end. But that was the start of everything, really.
"So it's made me really emotional. But I will beat this. I will beat it."
In an accompanying caption, she wrote: "I wanted to prove that age is just a number and I feel so proud of what I achieved. Just got to get through this real life trial now."
On Tuesday's episode, an emotional Callard was seen telling the other celebrities: "I didn't feel very well this morning. I had a bit of a funny turn and they've said I can't come back in. I've got to come out."
She added: "I don't want to go, I'm really sorry. I'm absolutely gutted. I wanted to finish. I wanted to prove that older women could do it."
She was consoled by campmates including ex-Gogglebox star Scarlett Moffatt.
After her departure, Moffatt told the cameras: "Selfishly, I would want Bev to stay, because she's like everyone's camp mam, but her health is more important."
Singer Sinitta said: "Beverley is my inspiration.
"You know that thing where you think, well, if Beverley can do it, I can do it. She gives me that. She's an amazing woman."
Meanwhile, there was more drama in Tuesday's episode when Adam Thomas furiously confronted Jimmy Bullard, after Bullard quit the show and appeared to get Thomas eliminated in the process.
The pair teamed up for a trial against their fellow campmates, with contestants told that the losing duo would leave the programme.
Former footballer Bullard didn't join in when the trial began, then said "I'm a celebrity get me out of here" to forfeit the challenge.
That left actor Thomas, who was covered in ants during his part of the challenge, fuming.
"Jim, don't do this bro, come on!" he shouted. "Is that how we're going out, yeah?"
Bullard apologised to Thomas, saying he'd "had enough".
Thomas then stormed out of his wooden cage and launched an expletive-laden rant at his partner before storming off. Bullard called his reaction "pathetic" in return.
"I just weren't feeling it," Bullard explained to the other contestants.
Thomas remonstrated with him further when they got back to camp. "What's up with you, bro? If you wanted to go... go. Don't take me with you. What is up with you? Tell me why.
"All you had to do is run through some mud and you said, 'I'm a celebrity get me out of here'."
Bullard replied that he wanted to go home, before an angry Thomas told him he should have quit on his own, or not done the show at all.
However, Thomas got a reprieve when hosts Ant and Dec gave the other campmates the choice of whether he should be allowed to remain, and they unanimously decided he should.
