Proud mom! Cynthia Nixon revealed that her eldest child is transgender.

“I’m so proud of my son Samuel Joseph Mozes (called Seph) who graduated college this month,” the Sex and the City alum captioned an Instagram photo on Friday, June 22, of herself and Seph at his University of Chicago graduation. “I salute him and everyone else marking today’s #TransDayofAction. #TDOA.”

Seph, 21, is Nixon’s eldest child. The actress shares Seph (born Samantha Mozes) and son Charles, 15, with her ex-partner Danny Mozes. She and wife Christine Marinoni also have son Max, 7.

Nixon, 52, tweeted about Trans Day of Action on Friday. “Happy #Pride! LGBTQ* people have greater visibility and acceptance than ever before, but members of the trans community are at a much higher risk of experiencing violence and discrimination,” she wrote. “Today, and every day, we stand with trans New Yorkers! #TransDayofAction #Dreamers.”

Nixon is running for governor of New York despite failing to secure the Democratic party’s endorsement in May. Incumbent Andrew Cuomo won more than 95 percent of the state party delegates’ vote. The political hopeful must get 15,000 signatures to earn a spot on the gubernatorial ballot.

“I’m not a protest candidate,” Nixon told the Daily News on May 23. “I’m a viable candidate who is really running hard for the Democratic nomination, and that’s why I’m here, to say this is my party, too, I’m not afraid and I’m here. You can’t shut me out.”Nixon reiterated her resolve on Twitter at the time: “I am attending the convention today because New York Democrats deserve to have at least one actual Democrat running for governor at their state convention. This campaign isn’t just about me. It’s about a Democratic Party that fights for its voters—not just its corporate donors. It’s about the communities tired of being beaten down and always put last. We’re ready to fight for a New York for all of us. We’re ready to fight for you!”