If you’ve ever walked down Fifth Avenue near the Met and looked at the spectacular mansions that still remain on the east side of the street, you’ve probably thought to yourself, “People don’t actually OWN those, right?” And your instinct is largely correct: Most of the gorgeous townhouses are actually occupied by embassies or schools or have been subdivided. In fact, it’s said that there’s only one privately owned residential mansion still left on that strip: the Duke-Semans house on 82nd, owned in recent years by real-estate magnate Tamir Sapir. (Until 2006 it was owned by descendants of the original owner, tobacco magnate Benjamin N. Duke, who had it built in 1901.) The Journal today reports that Sapir sold it — privately and not through a broker — to Mexican multi-billionaire Carlos Slim for $44 million dollars. And here’s the kicker: That astronomical price tag makes the spectacular townhouse only the fourth most expensive in New York.