Muse frontman Matt Bellamy and his wife Elle Evans are expecting their first child together.

The American model announced the happy news in an Instagram post on Sunday, sharing a snap of herself showing off her bump while standing alongside her husband, who had his hand placed lovingly on her stomach.

"Our little family is growing..... and so is my belly," Elle captioned the sweet image.

The 30-year-old also revealed that she and Matt, 41, had been keeping the news quiet for some time, adding in a post on her Instagram Stories: "Our best-kept secret since September."

The baby will be the first for Elle, while Matt shares eight-year-old son Bingham with his ex-fiancee Kate Hudson. The couple began dating in 2010, but called off their relationship in 2014, and have remained close friends and co-parents.

Elle and Matt started dating in 2015, with the British rocker popping the question in December 2017.

The couple tied the knot in a picturesque ceremony last August, and the blonde beauty has been sharing images from the big day on social media ever since.

"Two months of pure wedded bliss have flown by & it's time for appreciation posts to the people who worked tirelessly to make my dreams become reality," she shared in an Instagram post in October, before thanking her wedding planners, florists, hair and make-up team. "Thank you all for making the wedding of our dreams become our eternal reality."