Cynthia Nixon revealed her son Samuel is transgender in a sweet Instagram post on Friday

Cynthia Nixon revealed her son Samuel is transgender in a sweet Instagram post on Friday.

The candidate for New York governor, 52, shared an empowering message to her son Samuel — or Seph as he likes to be called — on Instagram during Trans Day of Action, June 22, with a #TBT 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,” Nixon wrote in the caption.

Samuel, 21, was born Samantha Mozes. Nixon shares Seph and 15-year-old son Charles Ezekiel Mozes with ex-husband Danny Mozes.

The former Sex and the City star is also mother to Max Ellington Nixon-Marinoni, 7, with her wife, Christine Marinoni. The couple married in 2012. Marinoni, an education organizer who has served as AQE director, met Nixon in 2001 when the actress was campaigning to reduce N.Y.C. public-school class sizes, per The Advocate.

The star is currently running for governor of New York against Andrew Cuomo, a Democrat, which she confirmed in March.

Nixon is a staunch advocate for LGBTQ rights, writing in a 2015 Variety op-ed about marriage equality, “We have to keep organizing like our lives depend on it.”

RELATED VIDEO: Sarah Jessica Parker Says She’s ‘Excited’ for Cynthia Nixon’s Governor Bid: ‘I’m Proud of Her’

She also addressed how critics freely called Sex and the City “groundbreaking,” writing, “When a TV show is “ground-breaking,” it doesn’t really create something new: It reflects something already happening in the population, but the culture hasn’t caught up with it.”

“Similarly, LGBT characters aren’t new; everybody has LGBT people in their family. And everybody needs to make the effort to come out in any and every way they can,” Nixon continued. “If people who are opposed to equality realized how many individuals they already like, admire or even love are LGBT, the battle would be over. It’s important to come out to our parents, children, co-workers, boss — you name it.”

She has been outspoken about a series of issues, including repairing New York City’s subway system, as well as abolishing ICE. On Thursday, she called it a “terrorist organization” while calling President Donald Trump “its egomaniacal leader.”