Hot party of the summer: Susan Magrino and younger sister, Allyn Magrino, are tossing an invitation-only thank-you bash next week at Bar SixtyFive at the Rainbow Room atop Rockefeller Center to celebrate 25 years since they took the plunge with Magrino PR.

Among the expected attendees are Susan’s husband, James Dunning, a media mogul who formerly owned Petersen Publishing and Ziff-Davis and once nearly bought the New York Mets and, of course, Magrino PR’s longest steady client, Martha Stewart.

Susan was a book publicist at Crown Publishing when she first encountered the Domestic Diva. Allyn Magrino was cutting her teeth as a publicist handling a foreign tourist office at a law firm representing Donald Trump.

“Every day is exciting,” said Susan Magrino. “It’s not just about media anymore. We do a lot more than we used to do because the world has changed.”