SEX and the City star Cynthia Nixon has become the latest Hollywood star to publicly acknowledge the changed gender status of a family member.

The 52-year-old actor, who is a candidate for the New York gubnertorial elections in November, made the declaration in an Instagram post on Friday.

Twenty-one-year-old Samuel, whose birth name was Samantha, was the first of two children Nixon had with her former partner Danny Mozes, whom she dated from 1988 to 2003.

In 2009 Nixon revealed she had become engaged to her same-sex partner, Christine Marinoni, and the couple welcomed their own child, Max, two years later.

"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," Nixon wrote on her Instagram post.

Samuel Mozes is far from being the first trans offspring of a celebrity parent.

Warren Beatty and Annette Bening's son Stephen reportedly began transitioning from female to male at the age of 14, while Chaz Bono (who was born Chastity) confirmed he had undergone gender transition in 2009.

Other celebrities, including Brad Pitt, Angelina Jolie and Pink, have discussed their desire to raise their kids outside of typical gender strictures.