In an interview published yesterday, Byrne said he was told who his real father was by a relative in 2002.
He said that after the discovery that his mother, Alice, had had a sexual relationship with her father, Patrick McShane, “everything fell into place”.
Byrne told the Times that his mother died in the 1980s after a long battle with mental illness, which he believes was brought on by her relationship with her father.
Byrne, who wrote the television series Tutti Frutti and its follow-up Your Cheatin’ Heart, went on to claim that his mother had made many trips to see her father when he was growing up and he now believes that she was in love with him.
He said his mother’s husband, Patrick Byrne, did not know about his wife’s relationship with her father.
“She was in love with her own father, utterly and totally. She just wanted to be in his company,” Byrne told the newspaper.
“She couldn’t even confess it. My own father [the man who brought him up] didn’t know.”
Immediately after being told the news, Byrne said he felt that he hated his grandfather but later reconciled himself to the facts.
“It’s because I admitted to myself that I adored my grandfather, beforehand,” he told the Times. “What did he do to me particularly that damaged me? I don’t think he did damage me.”
Byrne, who had two children during a long relationship with the actress Tilda Swinton, which ended in 2005, was the subject of a retrospective at the National Galleries of Scotland two years ago.