Cynthia Nixon's oldest child is transgender.

Cynthia Nixon and Seph (c) Instagram

Cynthia Nixon and Seph (c) Instagram

The 'Sex and the City' actress shared a heartfelt message on the Trans Day of Action (TDOA), in which she talked about how "proud" she is of 21-year-old Samuel, who is known as Seph and was named Samantha a birth.

Cynthia - who has Seph and 15-year-old Charles with ex-husband Danny Mozes, and seven-year-old Max with wife Christine Marinoni - shared a photo of herself with Seph at his University of Chicago commencement a few weeks ago.

She captioned the image: "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 (sic)"

The 53-year-old star - who is currently running for Governor of New York - later sent another message of support to the Trans community.

In a post that read: "If we had bluer democrats, there wouldn't be 75,000 trans dreamers whose lives will be in real danger if they get sent back to the birth countries they no longer even remember. (sic)"

She captioned the post: "Happy #Pride weekend! 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. Today, and every day, we stand with trans New Yorkers! #TransDayofAction #Dreamers (sic)"

Meanwhile, Cynthia previously revealed her children have mixed feelings about her campaign to take office in New York but they are still "very proud" of her.

She said in March: "I think they're excited on a certain level and dreading it on another.

"I think they are very proud. I think they are."

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