Sam Smith. Picture: Twitter

British singer Sam Smith has revealed his mother knew he was gay aged just three.

The 25-year-old singer-songwriter has revealed his mum Kate realised he was gay way before he came out at the age of 10, at which point his father Frederick started to fear he would get bullied for his sexuality.

READ: Sam Smith almost quit music

Reflecting on the track 'Him' from his upcoming second album, Sam shared: "The song is only semi-autobiographical. I came out when I was 10.

"I'd just finished primary school, going into secondary school, and I came out to my best friend when I was nine or 10.

"I was very sure of, and in, myself. When I told my mum she said she always knew, she said she knew when I was three, and my dad just asked if I was absolutely sure. And I was sure, even at that age, but they were incredibly supportive."

Sam explained that his father was especially worried about him, because he thought people outside their family might not be so accepting of his sexuality.

In an interview with Sir Elton John for Attitude magazine, Sam said: "I think my dad was scared for me, because of his own life experience.

"I think he saw a lot of kids get bullied and just felt really nervous for me."

Sam admitted his dad's fears escalated when the would-be star started to wear make-up to school.

The 'Stay with Me' hitmaker recalled: "Especially when, at 16 and 17, I used to wear a lot of make-up and dressed very differently at school. He didn't have a problem with it, but he was really worried about me."

Sam also admitted that he did, at times, receive some "awful" abuse because of his sexuality.

He said: "I've always said I wasn't [bullied], because I don't think my experience was as bad as others I've heard of, but when I look back at it now, it wasn't the easiest time.

"I was lucky, I had a very good group of friends around me, but some of the other boys could be absolutely awful to me at times. 

"It's nothing that has scarred me, though."