It’s official: Robert Saleh is back with the San Francisco 49ers.

The 49ers have re-hired Saleh as their defensive coordinator, Brian Costello from The Post confirmed. Saleh was previously let go by the Jets mid-season before being hired by the 49ers for a second time.

The Athletic reported on Thursday that Saleh was expected to return to his old stomping grounds.

The 45-year-old coach — who Jets owner Woody Johnson quickly fired after a 2-3 start — was a candidate for head-coaching jobs with the Jacksonville Jaguars, Dallas Cowboys and Las Vegas Raiders.

But once those three spots were filled, Saleh decided to return to the 49ers to try to rebuild their defense the dominance it had at the end of his first stint with the team.

The defensive coordinator job has been a revolving door for the 49ers, and Saleh will be fourth one in four seasons for Kyle Shanahan’s club.

DeMeco Ryans, who replaced Saleh in 2021, left to become head coach in Houston following the 2022 season, and Steve Wilks and Nick Sorensen were each replaced after one season the past two years.

Saleh was just 20-36 during his four seasons as the Jets’ head coach, but their defense was always strong under his tenure.

During Saleh’s last two full seasons in New York, the Jets ranked first in yards passing per game (178.9) and yards per play allowed (4.7).

They also were second in total defense (301.7 yards per game) during that time, but the defense imploded this season, especially after Jeff Ulbrich, Saleh’s defensive coordinator, was promoted to the head-coaching spot.

As for the Jets, they went the defensive coordinator route again, hiring Aaron Glenn on Wednesday as their head coach.

Glenn, a cornerback who played eight seasons with the Jets, had four successful seasons as the head of the Lions’ defense.

— with AP