Michael Bloomberg is quietly rejoining one of the upper-crust clubs he left over a decade ago when he first ran for office.

In 2001, the billionaire resigned from the Century Country Club in Westchester as well as the Harmonie Club, the Brook Club, and the Racquet and Tennis Club, while remaining a member of 10 other private clubs.

But Century members noticed a routine letter last month announcing new applicants that brought up Bloomy’s return.

“Dear Members: The following member has been proposed to rejoin the club,” it read, according to a source who saw it. “Please give the Membership Committee . . . any information you may have concerning this candidate.”

We assume he can cover the dues.