Cynthia Nixon reveals her oldest child is transgender

Actress Cynthia Nixon arrives at the 71st annual Tony Awards. (Reuters)

Cynthia Nixon is proud of her kids.

On Friday, the candidate for New York governor, 52, shared on Instagram that her oldest child, Samuel—known as Seph—is transgender.

Nixon shared the news in a post celebrating her son on the Trans Day of Action with a photo from his graduation earlier this month from the University of Chicago.

"I’m so proud of my son Samuel Joseph Mozes (called Seph) who graduated college this month. I salute him and everyone else marking today’s #TransDayofAction. #TDOA," the "Sex and the City" alum captioned a picture of the pair.

Nixon shares 21-year-old Samuel, who was born Samantha Mozes, with ex Danny Mozes. The former couple are also parents to 15-year-old son Charles Ezekiel Mozes. In addition, Nixon is mom to 7-year-old Max Ellington Nixon-Marinoni with her wife, Christine Marinoni.

In March, the star announced that she was throwing her hat in the ring for New York governor, taking on Democrat Andrew Cuomo.

"We want our government to work again. On health care, ending massive incarceration, fixing our broken subway," Nixon said in a video announcing her candidacy at the time. "We are sick of politicians who care more about headlines and power than they do about us."