Last November, Zayn opened up to the world when he revealed he was struggling with anxiety, and an eating disorder.
"When I look back at images of myself from around November 2014, before the final tour, I can see how ill I was," he told The Sun.
"Something I've never talked about in public before, but which I have come to terms with since leaving the band, is that I was suffering from an eating disorder.
"It wasn't as though I had any concerns about my weight or anything like that, I'd just go for days - sometimes two or three days straight - without eating anything at all. It got quite serious, although at the time I didn't recognise it for what it was."
Now, Harry is back in the limelight with his debut solo album, and while talking to the Sunday Times Magazine, he touched on Zayn's struggles.
"If anyone is ever going through anything, you always feel like you should know, so you could have done something. But it's not always how it goes, is it?
"In the same way that I don't talk about stuff, other people don't always talk about stuff, and maybe that's how they deal with stuff," he revealed.