Former Fire Commissioner Sal Cassano's son — who resigned in disgrace when The Post exposed his offensive tweets — will be rejoining the FDNY.

Joe Cassano, who left his job as a probationary EMT in March 2013, will be starting over at the FDNY's Emergency Medical Service Academy on July 13, the FDNY confirmed Thursday.

The younger Cassano, caught posting racist wisecracks online, was blasted by the mayor and his own dad.

"MLK could go kick rocks for all I care, but thanks for the time-and-a-half today, " Joe once tweeted.

He also posted anti-Semitic and crude comments about his patients.

"I like jews about as much as hitler," Joe tweeted.

His commissioner dad was appalled at his son's postings. "As a parent, this is very painful for me," Sal Cassano said at the time.

The FDNY would not address why Joe was allowed back into the department.