Tilda Swinton’s former partner has revealed that he is the child of an incestuous relationship – and described the union as "traditional."

Scottish artist John Byrne, 77, found out that his grandfather Patrick McShane was actually his dad after his aunt Helen died in 2002.

But after a period of hating his granddad, he has now come to accept his unusual lineage – and revealed that it’s not as uncommon as people might think.

He said: “I think he gave me that wonderful mixture of genes with his own daughter, the eldest of the family.

“That’s what they do in Ireland. I presume it’s what they do in unlettered places, and lettered places.

“It’s traditional, and nobody speaks about it.”

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As a child, John recalls that his mom would regularly walk eight miles from their home in Paisley to his grandparents’ house in Cardonald – and in hindsight it was because she loved him like a partner.

He said: “She was in love with her own father, utterly and totally.

“She just wanted to be in his company. She couldn’t even confess it.

“My own father [his mum’s husband Patrick Byrne] didn’t know.”

John, who was the brains behind Scottish TV series "Tutti Frutti," only discovered the shocking truth about his parentage when his cousin Aileen Kane called his and Tilda‘s remote Scottish home to tell him that her mom had passed away.

Speaking to The UK Times, he said: “Helen told Aileen what my mother had told her, when she was much younger.

"Aileen asked Tilda, 'Do you think I should tell [him]?' Tilda said, 'You’ve got to tell him.' She called me in and handed me the phone."

However, his cousin didn't deliver the news over the phone, instead meeting in Glasgow to tell him face to face.

John's mom died in the 1980s after a long battle with mental illness, which in hindsight John thinks stemmed from her incestuous relationship.

The Scotsman, who has two children with "Narnia" star Tilda, admitted that he felt hatred for his grandfather after the truth about his parentage came out - but slowly "everything fell into place".

He said that his attitude went from “he died of cancer, hell mend him” to realizing that he had only ever felt love for the man.

John, who met Tilda in 1985, added: "It’s because I admitted to myself that I adored my grandfather, beforehand.

“What did he do to me particularly, that damaged me? I don’t think he did damage me."

John and Tilda split up in 2005 but continued to live together for years, looking after the couple's 17-year-old twins Xavier and Honor in Scotland while Tilda worked on a string of blockbusters.

In 2008 she moved in a younger lover, Sandro Kopp - who is 18 years her junior - and the trio co-habited.

Speaking about the unusual arrangement, Tilda said: "The father of my children and I are good friends and I’m now in a very happy other relationship.

"And we’re all really good friends. It’s a very happy situation.

"Life doesn’t have to be complicated. You just have to have compassion with yourself and stop blaming yourself when things do get complicated."

This article originally appeared in The Sun.