The genealogy series Who Do You Think You Are? has turned from a family tree into a money tree for the BBC.
The first run went out, unassumingly enough, on BBC2 in 2004, kicking off with Goodie-turned-wildlife presenter Bill Oddie.
Fast-forward six years and seven series and WDYTYA? is now not only one of the top-rated programmes on the more mainstream BBC1, to where it switched after the second series, but also a massively successful international franchise on a scale to rival Big Brother and Who Wants To Be a Millionaire?.
There are now versions of the series in Canada, America, Sweden, Australia, South Africa, Poland and, of course, Ireland, where we've so far had two seasons on RTE1. Clearly, celebrity + genealogy = TV gold.
Well, maybe not always. Given such a level of saturation, it's inevitable you're going to uncover a few duds among the nuggets. The RTE episode featuring radio broadcaster, bookie and former politician Ivan Yates might have been fascinating for him, but it was rather less compelling for the rest of us.
On the American version, meanwhile, Sarah Jessica Parker uttered so many orgasmic "Wows" and "Omigods" (often over something as mundane as the hill in Dakota a miner ancestor once toiled on) that if you closed your eyes, you could have been listening to badly-dubbed Swedish porn.
But when the series strikes gold, it strikes it in abundance, and the version with the highest hit rate so far is the BBC's. Last night's subject was comedian and actor Alexander Armstrong.
Ironically, Armstrong appeared in a brilliant sketch spoofing WDYTYA? on The Armstrong & Miller Show, in which he discovered, to his horror, that he was descended from a long line of prostitutes.
No such skeletons rattling around the cupboard in the real thing, though.
Armstrong is, not to put too fine a point on it, a bit of a toff anyway, but even he was genuinely taken aback to learn his lineage stretched back to William the Conqueror.
A relation called Edward Somerset, 10 or 12 generations removed, had been a soldier and spy during the English Civil War, and had also invented a water-powered machine nearly 200 years before the arrival of the Steam Age proper.
This was a fascinating episode and seemed to prove a rule about Who Do You Think You Are? -- at least in its British incarnation. Namely, the posher you are, the more interesting your family history is likely to be. Just ask poor Yorkshire peasant Michael Parkinson, who was supposed to feature on WDYTYA? last year, until researchers discovered the history of the Parkinson clan was too boring.
It's rare you come across two cracking sitcoms on the same night. But this is not one of those rare weeks. On the plus side, Simon Amstell's Grandma's House, despite its obvious debt to both The Royle Family and Seinfeld, gets better by the week.
This was the third episode and by now the characters -- the best of them being Simon's mother's hideous boyfriend Clive and his grandad, whose cancer may or may not be real -- are well-established and familiar.
I'm not sure if Amstell himself has suddenly discovered how to act, or if he's just feeling more comfortable in his sitcom skin, but something is sparking nicely here.
To bring us swiftly on to a downward slope, there's The Adventures of Daniel. Like Grandma's House, this is written by and stars a comedian playing a barely disguised version of himself -- in this case, 19-year-old Scot Daniel Sloss. Unlike Grandma's House, it's almost doggedly unfunny.
Who do you think you are? ****
Grandma's House ****
The Adventures of Daniel *