5 Seconds of Summer star Luke Hemmings has become a father for the first time

They captioned the post, which featured blurry photos of the baby: "Our best kept secret. Written and Produced by Sierra and Luke Hemmings."

Luke explained why the couple - who are thought to have married in 2022 - had chosen to keep their happy news a secret in the comments.

He said: "In our perfect world, we'd keep our daughter a secret forever... for similar reasons we chose to never share our wedding photos from years ago.

"However, going into this next album cycle I'm very aware that her existence would inevitably leak."

The Australian musician continued: "To avoid any speculation, we're posting this now and humbly asking for everyone to respect her privacy.

"If you see us in public, please avoid taking or sharing photos of her as we don't plan on publicising her name, birthdate, or face any time in the near future.

"Thank you for understanding and for the support. All our love, The Hemmings."

Luke released the solo EP Boy last year and explained how he hoped that it would help prepare him for fatherhood.

He told Rolling Stone Australia: "As I get older and (am) thinking about having kids at some point, I'm reflecting on myself at that age, still being that struggling boy deep down inside.

"There can be a tendency, especially for men as they get older, to bottle things up inside and not address them until it's maybe past the point of no return.

"This EP is about uncovering emotions or experiences from my younger years, getting in touch with that inner boy, that inner child, so to speak, in order to become a fully realised version of myself."

Luke explained that he writes music "in short bursts" when working solo.

He said: "I write in short bursts, over different periods of life.

"Sometimes I'll start a song and then come back to it months later to finish it. But lately, I've been trying to get across more emotion with less words. In the past, I've tended to overcomplicate things lyrically by saying too much. A lot of these new songs aim to be as concise as possible."