Sam Smith is among the first celebrities to ask the public to refer to them using they/them pronouns.
The How Do You Sleep? singer came out as non-binary in early 2019, sparking a debate over gender and sexuality.
What have they said?
In October 2017, Smith spoke for the first time about their gender in an interview with LGBT publication Attitude.
“I feel just as much a woman as I am a man,” they told the magazine.
Later that month, in an interview with The Sunday Times, Smith came out as genderqueer, saying that they had never seen themselves as being a typical man.
Smith also admitted that as a teenager they had owned mostly female clothing and wore make-up to school.
In March 2019 the singer appeared on actress and activist Jameela Jamil’s podcast about fame, body image and confidence.
Smith told her: “I’ve always had a little bit of a war going within my body and my mind.
“I do think like a woman sometimes, in my head. Sometimes I’ve questioned ‘Do I want a sex change?’
“It’s something I still think about, like, ‘Do I want to?'”
Which other celebrities identify as non-binary?
Stars who have said they identify as non-binary include Me Too campaigner Rose McGowan, Queer Eye star Jonathan Van Ness, drag queen Courtney Act and musician Grimes.
Miley Cyrus and Cara Delevingne, however, identify as genderfluid, which differs from non-binary in that the person does not identify as having a fixed gender.
Rather they experience shifts or changes in gender from male to female over time and mood.
What have they said about it?
As well as identifying as genderfluid, Delevingne is bisexual and has dated actress Michelle Rodriguez and singers Jake Bugg and St Vincent.
In an interview with Vogue, the catwalk star said: “When I first realised that gender is so much more fluid than masculine or feminine it was a breakthrough moment for me.”
McGowan, one of the first to accuse Harvey Weinstein of sexual misconduct, came out as non-binary in March 2018.
“I think we’re never going to solve anything by going into the man/woman construct. Step back to humanity,” the actress said on the Love Alexi podcast at the time.