Hilary Duff has revealed she's pregnant with her fourth child!

The Lizzie McGuire star already has three children, and this wonderful new addition will be her third child with Matthew Koma.

She is mum to Luca, 11 - who she shares with ex husband Mike Comrie - as well as daughters Banks, 5, and Mae, 2, whom she shares with her current music producer husband Matthew.

Taking to Instagram on Tuesday, Duff shared a family photo in which she shows off her growing baby bump.

The frame of the card reads: "So much for silent nights" and the star captioned the post "Surprise surprise."

She then shows the back of the card, which contains a photo collage featuring individual pictures of the kids, which says: "Buckle up Buttercups, we're adding one more crazy to this crazy bunch. The Duff, Bair, Comrie Crew."

Fans and celebrity friends all rushed to wish the 36-year-old the best on her latest addition to the family.

Jenna Dewan took to the comments and wrote: "Ahh congrats !!!" Meanwhile, other big names posting their well wishes to the star include Elle and Dakota Fanning, Lucy Hale and Jaclyn Hill - to name a few.

The star has yet to reveal how far along she is and when her due date is.

We wish her the very very best!

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