John Byrne is a playwright and artist, the man who created the cover for The Beatles Ballads album and wrote the TV series Tutti Frutti and Your Cheatin' Heart. He is also the former partner of actress Tilda Swinton, with whom he has two children.
Born in Scotland, his family are originally Irish, and last week Byrne revealed that he is the child of an incestuous relationship between his mother, Alice McShane, and her father Patrick - meaning that John's father is also his grandfather.
"That's what they do in Ireland," he said. "I presume it's what they do in unlettered places and lettered places. It's traditional, and nobody speaks about it."
Quite apart from the creepy suggestion that incest is "traditional" here, just "what they do in Ireland", John, who says he initially hated his grandfather on hearing the story of his origins but then came to love him, is pitching the relationship as a loving and, therefore, presumably consensual one.
"I think he gave me that wonderful mixture of genes with his own daughter, the eldest of the family," he said, adding of his mother: "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."
His mother's husband, Patrick Byrne, apparently, never knew that he was not in fact John's father.
Byrne's mother, who died in the 1980s, had a long history of mental illness, something Byrne said he believes was a result of being so "utterly and totally" in love with her own father. The mental illness may well have been caused by Alice's relationship with her father, but that it was simply the product of some kind of intense love that dared not speak its name is deeply questionable.
As a writer and artist, John undoubtedly has an original and creative take on the world around him, and he is, of course, entitled to read his own story however he wants. "What did he do to me particularly that damaged me? I don't think he did damage me," he said of his grandfather.
That reading of a strange, and, to the rest of us, horrible, situation is his prerogative.
But the idea that incest can ever be pitched as something consensual, a "wonderful mixture of genes", and part of a loving relationship, is far more troublesome, and dangerous. Perhaps particularly in Ireland.
Because though there is nothing "traditional" about incest in this country, there is no doubt that for way too long we failed to stand up for the fact that the victims of incest are, always, just that - victims. They are not complicit. They are not willing. They are not ever, in any way, responsible for the abuse. And abuse it is.
No matter how you dress it up as "love" - and indeed so complex are human relationships that there may very well be love in there somewhere - incest is always an abuse. Of power, of trust, of authority, of youth and vulnerability. Not for nothing do most of us consider it the most heinous of crimes.
And, therefore, the idea that there may be an alternative narrative - a loving, consensual incestuous relationship - besides not bearing up to any kind of close scrutiny, is a thin end, wedged into the acceptance that incest is always wrong. And once there is any kind of crack in that edifice, there will always be someone mad enough, bad enough, to exploit it.
Byrne isn't the first to suggest that incest can be something sanitised and agreeable. In 2009, Mackenzie Phillips, a former child actor and daughter of John Phillips of folk rock band The Mamas and The Papas, said she had a 10-year consensual affair with her father - a man so famously off-the-rails that Keith Richards once kicked him out of his house for being too out of it.
The affair, Mackenzie said, lasted through her marriage, aged 19, and ended only when Mackenzie discovered she was pregnant, and feared the baby was Phillips's. Phillips, she said, paid for an abortion.
But for all that Mackenzie described the relationship as 'consensual', she also said that it began with rape, in a hotel room in the late 1970s, when she was 19. Mackenzie had passed out after a drug binge and later "woke up that night from a blackout to find myself having sex with my father. I don't know how it started..."
She added: "After the first experience, I went to my father and said we need to talk about how you raped me. My dad said: 'Raped you? Don't you mean made love?' In that moment, I thought I'm really on my own here."
Somehow, Mackenzie reframed that experience, temporarily anyway, and continued to do drugs and have sex with her father. But despite describing the relationship as an affair, she also said: "No matter what kind of incest, it is an abuse of power... a betrayal of trust."
And that, of course, is the point. Not everyone believed Mackenzie, who spoke out only after John died. Her long history of drug abuse and mental health issues were used against her - although they could just as convincingly be used for her - with the suggestion that this was a fantasy or some kind of attention-getting ploy. Naturally, Mackenzie had no 'proof' of her story - by its very nature, incest is something hidden - and her own deep and painful confusion may have given some comfort to those who rejected her claims.
For as long as there is any kind of ambiguity whatsoever around incest - this idea that it can ever be acceptable or consensual, ever not be abuse of the worst kind - there will be people who will use this to justify themselves. Which is precisely why we need to not allow these faint suggestions to creep in.
In the case of John Byrne, he is entitled to say that his grandfather didn't "damage" him - that is his truth, his myth of origin - but the idea that Patrick McShane didn't damage his daughter is unacceptable.