Cityfile encountered a stubborn mystery this week: Why did Huffington Post co-founder Ken Lerer help People magazine reporter Joey Bartolomeo buy a $1 million Upper East Side apartment? Bartolomeo and Lerer were mum, but we've found a (mundane!) answer.

He's her uncle. Or so we're told.

Last week, Cityfile noticed a Blockshopper report that Lerer had gone in with Bartolomeo on $1,025,000 apartment in Carnegie Hill. They thought that was pretty weird—Huffington Post doesn't pay its own writers, but its co-founder buys real estate for People writers? The mystery deepened when Cityfile started digging, and found that Lerer helped Joey's sister Stephanie buy a $1.25 million apartment on the Upper West Side in March. What is it with Lerer and the Bartolomeo girls, Cityfile wondered. (Well, the Stephanie Bartolomeo connection makes some sense—she works in ad sales at Huffington Post and worked with Lerer when he was at AOL. But still.)

Do the Bartolomeo girls possess some horribly embarrassing secret that they've been using to blackmail Lerer? Is Lerer carrying on a tawdry affair with both sisters at the same time?

Things only got stranger when Cityfile put in calls to get an answer—first Joey stonewalled, then Lerer stonewalled, then a Huffington Post flack stonewalled. No one would answer the simple question: Why is Ken Lerer buying apartments for Joey and Stephanie Bartolomeo?

Anyway, the answer is: Because he's their uncle. Or so a source who knows them told us. Either their stepfather's brother or their mother's brother; our source isn't quite sure. So there's that. Mystery solved. We could use an uncle like that.

The only remaining mystery, of course, is why Bartolomeo and Lerer would insist on being so cagey about a mundane real estate transaction.

We e-mailed Joey to confirm, but haven't heard back yet.

UPDATE: "Yes, he's our uncle and he's the best uncle in the galaxy," writes Bartolomeo. We concur.