Olly Alexander was told not to come out when he first found fame.
The Years & Years frontman claims he was told not to talk about his sexuality publicly but he soon "ignored" the advice.
He said: "What happened after we signed was, we got offered media training. One afternoon I met a very nice lady whose job was to help us answer questions in interviews - give us tips, tell us what journalists might try to trip us up on. I asked her what she thought about me being gay.
"She said - with very good intentions I'm sure - 'Why does anybody need to know about your sexuality? What business is it who you go to bed with? Do you really want to invite personal questions like that? Maybe it's better to not say anything about your sexuality at all.'"
And the 'Desire' hitmaker felt it was important to be "open and honest" about his sexuality, to inspire others who were struggling to come out.
Speaking at LGBT charity Stonewall's fundraiser, he added: "The moment came when a journalist did ask me what my sexuality was, and I said, yes, I'm gay, this song is about a man. It was a really big moment for me, and I realised I needed to say that for my 15-year-old self. I needed to say to him, look, we are not hiding any more.
"I saw first-hand how being open and honest and vulnerable in myself inspired that in others. I got so many messages from fans who wanted to share their story, who were struggling with their sexuality or gender identity, had problems at school or at home."