The city Conflicts of Interest Board yesterday fined a former FDNY supervisor $12,500 for approving staggering overtime pay for his son-in-law over two years.

Robert Zerillo admitted approving a lucrative OT tab for his son-in-law in 2009 and 2010, COIB said. The son-in-law, Leonardo Labella, also agreed to pay a fine of $1,500.

The Post reported last year that Labella pocketed $207,146 in 2009, including $112,350 in OT, for repairing street fire-alarm boxes. He ranked second in city OT that year.

Zerillo, now retired, who was supervising Labella at the time, ranked third in 2009, taking home $111,451 in OT.