Living in the world’s most fame-obsessed city, Louis has got used to being ignored at LA’s glitzy showbiz parties.
But the shallow locals who scan the room for someone more famous to talk to when they meet him would probably change their minds if they knew the gangling Brit is related to Hollywood royalty.
“We’ve met a few times,” he says. “Jen is a really nice person.
“I hope her and Justin do get married but I don’t have any dates or anything like that. It would be nice to be there if they did.”
If Louis is at the celeb wedding of the decade, he must hope it’s a friendlier experience than the handful of exclusive parties he’s been invited to during his time in Los Angeles.
“I have been to a few A-list parties,” he says. “I’m a fan and I’m starstruck like everyone else. It’s weird, though.
“You can talk to someone relatively famous and they say, ‘What do you do? What do you do for a job?’ and I say, ‘I make documentaries for the BBC’ and you see their eyes just glaze over.
“And then you think they just want to get rid of you.”
Louis moved to California last year to make his hit new BBC2 series LA Stories.
Viewers have already seen his film about the city’s stray dog epidemic and a moving look at how the famous Cedars-Sinai Medical Centre deals with terminally ill patients. He has also reported on how America houses sex offenders.
Not exactly glitz and glamour, but Louis says he was determined to provide a different insight into American life, and so after his wife Nancy complained of the appalling British weather the couple, along with their two young children, moved to LA.
He told The Mirror: “They may not be the subjects you immediately think of when you think of LA but they struck a chord with me.
“Things like life and death or what to do with sex offenders, the sort of subjects that are borderline taboo and I think the feeling was that by doing them in LA we would get a different side of those stories and experience a different side of Los Angeles.”
Now he has finished filming though, Louis, son of American writer Paul Theroux, says he is ready to return home to London.
“There are so many differences between here and back home,” he says.
“LA is the opposite of Britain in a lot of respects and that’s what draws so many British people here.
“You’ve got sun, space, you’ve got wide open roads, you’ve got mountains and deserts, and probably the biggest thing is cultural.
“You have the permission to be, feel, do and say what you like without worrying someone is going to say, ‘Stop being such a dick’.
“You can say, ‘I am a poet, rock-climbing shaman, and my name is Hiawatha Moonbeam’ and people in America will say, ‘Hey, that’s great. All power to you man’.
“In Britain they’d say, ‘What’s happened to Louis, he’s going round like a loon’.
“There are merits to both ways of doing things but it definitely feels when you are here you can open up a bit more and reinvent yourself.
“But I miss Britain a lot. I miss going on the tube, I miss Radio 4, I miss University Challenge, I miss going out and bumping into people.
“You don’t really bump into people on the freeway. I miss the sense of humour.
“We are ready to move back to Britain as a family. It’s just a case of deciding we had a great adventure and now it’s time to go back.
“Our families are back there and most of our friends. And the kids miss their real friends.”
Louis puts his success down to his British manners, believing any question can be asked as long as it is done so politely.
“I feel you ask the question you need to ask but if you ask in a polite way you get away with it,” he says.
“They used to say about Alan Whicker that he used to ask polite questions but he asked the right questions so it’s something you just have to do.
“Sometimes the best things I do in the documentary are things that I do by not being slick, by being bumbling or showing fear or being awkward or not quite handling a situation, and that comes across sometimes with more impact.
“There is a certain realness in it.
“When I first got my first job in TV it was with Michael Moore, the American documentary maker.
“I thought he was giving me the job because he thought, ‘He’s kind of funny and intelligent’.
“Now I look back and realise he just saw that I was a sort of incongruous figure, like a kind of stick-like, bespectacled English nerd who would make a funny contrast with some extreme Americans.”
Talking about what he would like to tackle in the future, Louis he explains he is not averse to making one-off When Louis met… programmes if he felt the subject was right. Specifically, if the subject was Charlie Sheen.
“We are always open to that person I could get to know and do that single programme on,” he says.
“Ever since he had that public meltdown I have been approaching Charlie Sheen. Once every 10 months I think again, ‘Ah, what about Charlie Sheen?’.
“Although I have not spoken to him directly I did send him a letter. ‘Dear Charlie, I am fascinated by you, let’s make a documentary. Yours, Louis Theroux’, but nothing came back.
“I feel we would give him a really good forum to discuss things he is interested in.
“Despite some of his outbursts being a bit zany, he is also a very intelligent man with an interesting take on the industry.”
The next episode of Louis Theroux’s LA Stories, Among the Sex Offenders, is on Sunday, April 6 at 9.00pm on BBC2.