Terminal cancer sufferer and charity fundraiser Jane Tomlinson said she has been subjected to abuse from people who question her illness.
Jane Tomlinson is now too ill to train for more physical challenges
The radiographer from Leeds, who was diagnosed with breast cancer in 2000, has raised about £1.5m through a series of gruelling physical challenges.
But in an ITV documentary to be broadcast on Tuesday Mrs Tomlinson, 43, reveals some people doubt her illness.
She said abusive phone callers had accused her of "faking" cancer.
Mrs Tomlinson reveals in the programme how one caller said: "You are nothing but a ... fraud. You no more have cancer than I have."
She added that her family had taken several phone calls from more than one person, but one caller in particular had been quite unpleasant.
Mrs Tomlinson has drawn praise from across the world for her feats of endurance, including a 4,200-mile bike ride across America, taking part in the Florida Iron Man contest and cycling from Rome to her home in Leeds, West Yorkshire.
"I have heard people say I can't possibly be ill and do the things I do and there can be nothing further from the truth.
"Yes, I am very ill and yes, I have done the things I have done and no it hasn't been easy, and just because I smile through it, it doesn't mean it doesn't hurt because it does - it hurts an awful lot."
Mrs Tomlinson's husband Mike told the programme: "I think if we weren't raising money we wouldn't do it because it is way too big a price for an individual family to pay.
"We have been really lucky - she's lived 14 times longer than we expected."
Mrs Tomlinson said she was now too ill to train for further challenges, but said she was supporting the "Run for All" event, a 10-kilometre run in Leeds on 24 June.
The programme, No Surrender, is broadcast on ITV1 in the Yorkshire region at 1930 BST on Tuesday.