Michael McIntyre, 38, was brought up believing his father Ray Cameron had died of a heart attack, and only discovered that he had killed himself four years ago.
"I’m heartbroken my stepmother has chosen to share painful and personal information publicly"
His father, who suffered from depression following a downturn in his comedy career, shot himself in the head in 1993, aged 55.
His widow Holly, now 58, decided to shield the truth from Michael, who was only 17 at the time, and his 15-year-old sister Lucy.
But, yesterday, she revealed that she was forced to tell her two step-children the truth in 2010 after Michael was invited to take part in BBC show 'Who Do You Think You Are?'.
She feared Cameron's death certificate - which states that he died of a ‘self-inflicted gunshot wound to head’ - would be found, revealing the real cause of death to Michael.
Speaking with The Mail on Sunday, she said: "He emailed me and said he would be doing this show and could I help the BBC with information about his daddy.
"I knew the researchers would find the death certificate because it is a matter of public record. I had to come clean."
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She added: "That was the hardest phone call of my life. I was shaking when I told him. For years I kept this terrible secret and finally I was sharing it.
"I said, 'Michael, your father didn’t have a heart attack. He killed himself.'
"There was a paralysed silence on the other end of the line. He was crushed. How are you supposed to react to news like that?
"He just said, 'Oh my God, Oh my God… are you sure?'"
Holly justified her decision to speak out about the intensely private matter by saying that Michael did not ask her permission when he revealed personal family stories in his 2010 autobiography.
She also claimed that she and Michael fell out over his apparent refusal to help the career of half-brother Billy, an aspiring musician.
Holly said Michael told her: “This is strike one. You know what happens when you get to strike three? You’re out, Holly.”
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Holly said strike two was a couple of years ago when she gave a quote to a journalist about Michael, who is married to Kitty.
The interview with a Sunday paper about the suicide “will be strike three”.
But Holly added: “I have lived with the guilt, the secrets, for so long. It’s been a toxic element in my life, in all our lives.
"I tried to honour Cameron’s wish to protect the kids for as long as I could. Now it is time for the truth to be set free.”
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Yesterday, Michael McIntyre said: "I’m heartbroken my stepmother has chosen to share painful and personal information publicly."