With a surname like Theroux, he has to be a relative, right? Well, there's famous travel writer father Paul, who sat on international trains for most of the 1970s and pontificated in varying degrees of rudeness about his fellow passengers. There's also brother Louis, master of esoteric television documentaries, curious about everything from American swingers to sad old men hooking up with Third World brides.
And Marcel Theroux? He's just published his second novel, The Paperchase, the plot of which focuses on the rivalry between two brothers and a difficult relationship with a successful and mostly absent father. Work that out.
It is, of course, deeply unfair to the son, but having read most of the father's travel books, I did wonder - while waiting hotel for Marcel Theroux to appear from his photo-session - if professional impoliteness runs in genes.
If it does, it appears to have skipped this generation. Theroux the younger is a charmer - funny, bright, full of stories and a good listener to questions. He's the sort of person you always hope you'll be sitting next to on a long flight but, alas, never are. This is only his second time in Ireland; the first is recorded in one of Theroux senior's books, in which he recounts a family visit during the 1970s to the Great Blasket.
"I was only six or seven, but it made a big impression on me," he says. "Going out in that little boat. Seeing all the deserted houses."
The Blaskets are mentioned briefly in The Paperchase, when the character Damien March imagines a flight across the Atlantic from London to Boston, and looking down over the deserted Blaskets. It's a tiny but telling detail. Only someone who had actually been there and had affection for the place would put it in.
"Wasn't there a writer who lived there once?" he asks.
"Peig," I say, with a grimace.
"No, not that one. The one who wrote Twenty Years A-Growing?"
I confirm the existence of Maurice O'Sullivan.
"Why did you look sort of odd when you said the other name?"
I give a brief explanation of Peig's Irish-language contribution to my generation of schoolchildren. Theroux considers this. "If she'd only written it in English, it would have been the first Angela's Ashes," he observes, which is a remarkably fresh way of looking at Peig's unhappy opus.
The question Marcel gets asked most often in general is: does he find it a help or a hindrance having a father who's a writer? And, as regards this second novel, do you get on with your brother? He is fairly cagey about the father question. It can't be easy (unless you're Martin Amis) to aspire to the job your father has done before you. Grand if you're in a profession such as law but anything creative is another matter entirely.
"I think Dad likes the book. He says he does. I don't know if he means it though," he says.
Marcel himself has stopped reading his father's fiction. "I would be afraid . . ." He's not sure what he's trying to say, even though he must be asked this all the time. He starts again. "I would be afraid of being influenced, or that people would think I was being influenced."
Of the two brothers, Marcel is older. Yet it's Louis who got the break in television that Marcel was looking for. The older brother, like the character in his novel, worked graveyard shifts in the BBC newsroom for some years without it ever transforming into something more, well, exotic. It was Louis who ended up presenting those wonderfully odd programmes, Louis Theroux's Weird Weekends, and who is currently shadowing Neil and Christine Hamiliton for one of his profile specials.
The day Marcel was in Dublin, Louis Theroux was in London at the Hamiltons' side as they were being questioned about the bizarre sex allegations. Every British newspaper and television station had them on the front page or at the top of a newscast. If you looked at some of the coverage closely, you could see Louis in the background, looking slightly dazed at the documentary-maker's good fortune of seeing his subjects become hot news as they are being tracked.
In every interview Marcel has given in the past couple of days he has been asked if there was any news from Louis on the Hamiltons. When you consider that he is giving interviews because he has published a book, it is rough luck that what everyone wants to talk about is the brother.
"It was contrived to overshadow the publication of my book!" Theroux says, but he says it with a laugh. Besides, he knows that reporters will never miss a news angle.
The novel itself is about a 35-year-old reporter who has been left a museum-like house by an American uncle. Fed up with his job and getting on badly with his only sibling, brother Vivian, and his father, he takes off to live in the house, on an island off Cape Cod. There he discovers a manuscript written by his reclusive uncle, which turns out to be more fact than fiction.
"I don't write full-time," he says. "I went part-time to write the first book." He admits it was "a little bit painful" in the beginning seeing the younger brother he refers to as "Lou" streak ahead of him. "But when I saw him, it was impossible to be jealous. He was just being Louis. Curious and always sort of in the background. He got that from Dad. That's how we always were around him."
However, although it may not be as much an ego-boost as having your own show on prime-time television, Marcel Theroux is hardly making the tea for a living. He has presented several travel and social-history documentaries for the Discovery and National Geographic channels, as well as writing travel articles for US magazines. Last month, he was in Chechnya, where he was making a programme about human rights for Channel 4.
So have the brothers ever considered joining up with their father on a project? Yes, it turns out that Marcel Theroux has a wheeze he'd love to see happen. In Paul Theroux's first and possibly most-read travel book, The Great Railway Bazaar, part of the action is on the Trans-Siberian Express.
"It would be great if the three of us went on the Trans-Siberian together. Dad could just be Dad, Louis could make the documentary, and I could translate." Translate?
"I speak Russian," he says off-handedly. "That way, we'd all have a role."
It is indeed a compelling concept, with the promise of some great television moments from the Theroux trio, and I sincerely hope we see it on our screens sometime very soon indeed.
The Paperchase, by Marcel Theroux, is published by Abacus at £9.99 in UK