Out actress and gubernatorial candidate Cynthia Nixon said Friday that her oldest child is transgender.

The 52-year-old Nixon shared the news in an Instagram post during the Trans Day of Action.

“I'm so proud of my son Samuel Joseph Mozes (called Seph) who graduated college this month,” Nixon captioned a photo of herself and Seph at his graduation from the University of Chicago. “I salute him and everyone else marking today's #TransDayofAction. #TDOA.”

Nixon shares custody of Seph and Charles with her former boyfriend of 15 years, Danny Mozes.

Nixon married education organizer Christine Marinoni in 2012. They welcomed daughter Max Ellington Nixon-Marinoni in 2011.

The former Sex and the City star is campaigning for the Democratic nomination for governor of New York against Governor Andrew Cuomo and Greg Waltman. The primary will be held on September 3.