Calvin Klein’s 22-year-old ex-boyfriend claims he’s being stalked by private investigators hired by the iconic fashion designer. Nick Gruber, who carried on a 2 1/2-year relationship with Klein, 69, until three months ago, said he’s been approached by private investigators in LA and New York for more than a month who claim to have information on his new boyfriend, Hollywood animator John Luciano. The two were approached last night at downtown Manhattan restaurant Toy by a man who identified himself as being a private investigator with questions about whether Luciano has a connection to notorious mobster Charles “Lucky” Luciano. “The investigator showed up at my table and started harassing me and my [boyfriend]. He said, ‘Your boyfriend is in the mob and is being followed by the feds.’ Then this morning he showed up at my hotel,” Gruber told The Post’s Tara Palmeri. “Calvin can hire goons to follow John and me all he wants — we have nothing to hide. I’ve moved on. I’ve never been happier.” Gruber said the investigator followed him in a car to the airport and boarded with him on his Virgin America flight to LA on Tuesday. Meanwhile, a source told Page Six that Klein has hired detectives because the designer believes that, “Luciano and Gruber are involved in various unsavory business activities intended to embarrass him.” Gruber has previously said he intends to write a book and film a reality show dishing all about his relationship with Klein.