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“Mad Men” star January Jones is dating “The Bachelor” star Nick Viall, according to a source.

Jones has just started dating Viall, who starred in the 21st season of “The Bachelor” in March, during which he got engaged to contestant Vanessa Grimaldi. He and Grimaldi split just months later, in August.

A source exclusively tells Page Six that Jones and Viall got together after she admitted on “The Late Late Show With James Corden” that she was a “Bachelor” superfan.

“They’ve been dating for about two months. She went on ‘The Late Show’ in ­mid-November and said Nick had reached out to her and tried to get her to lip-sync battle with him. She declined, but then he asked her out to a drink and she accepted. They’ve been seeing each other since,” the source said.

Jones celebrated her 40th birthday with Viall and some of her former “Mad Men” co-stars at Inkwell in LA on Saturday.

Jones had joked to Corden of Viall, “You don’t know if you like him or if he’s a scumbag, but that’s why I’m attracted to him, maybe.”

Reps didn’t get back to us.