Jill Zarin is reuniting “Real Housewives” from various cities and seasons for her fifth annual Luxury Luncheon at her Southampton estate on July 29.

“It’s the unofficial ‘Housewives’ reunion,” a source said.

Zarin’s invited “all cast members from each franchise over all the years,” and she’s opening the luncheon to the public for the first time to benefit thyroid cancer research.

Her husband, Bobby, was first diagnosed in 2009. “Bobby continues to get stronger every day and will be back in Southampton for the summer,” Zarin’s rep said.