Hilary Duff has hinted she is working on new music.

Taking to Instagram on Wednesday, the actress-singer celebrated the 22nd anniversary of the release of her second studio album, Metamorphosis.

The project, which featured the singles So Yesterday and Come Clean, dropped on 26 August 2003.

"Clearly I had to go digging around the internet for pictures from this time as I'm not sure camera phones even existed. Sadly all my hairstyles ARE very documented," she captioned a carousel of images showing her promoting the album at the time. "I do know this marker of time was a huge change in my being. I was embarking on something I had no idea would make such an impact on people's lives, and mine."

And while Metamorphosis was popular with her fans, Hilary admitted some of the songs don't hold the "emotional depth I look for today".

"(But) I know my 14/15 year old self meant every word. It sure as hell also landed on people at the right moment in time and set me off on a pretty epic adventure," the 37-year-old continued. "Yesterday marked the 22nd anniversary of Metamorphosis... Although these are distant memories for me, thank you for showing up the way that you did."

Hilary concluded her message by hinting there may be a follow-up in the works.

"To be continued...," she teased, adding a string of butterfly emojis.

The Younger star, who is married to music producer Matthew Koma, released her fifth studio album, Breathe In. Breathe Out., back in June 2015.