Robin Thicke and April Love Geary are expecting their second child together - just six months after she gave birth to their daughter.

The couple let six-month-old Mia break the news to the world as April shared a short video of their little one waving her ultrasound scan picture around, and revealed the youngster is going to have a sibling.

April captioned the clip on Instagram: ''Well someone is going to be a big sister next year! We're so excited to share with y'all that I'm expecting again! (sic)''

The pair's baby is due on March 10, 2019, which will be Robin's 42nd birthday, and they will find out whether they are expecting a brother or sister for Mia over the weekend.

She added: ''We find out Saturday if it's a boy or a girl! What do you guys think it's going to be? Forgot to mention the due date is Robins birthday! (sic)''

In the clip, April asks Mia: ''What are you holding? Is that your little baby brother or sister? What do you think? Are you excited?''

The little one seemed delighted at the thought of having a brother or sister because she couldn't stop smiling throughout the clip.

In February, Robin - who already has eight-year-old son Julian with ex-wife Paula Patton - revealed April had given birth to Mia.

He shared a brief video of himself cradling their baby, and wrote: ''On 2/22 at 13:33 Mia Love Thicke was born. Thank you God and April Love! (sic)''

Mia was born earlier than expected as when April, 23, revealed last August that she was pregnant, she told her followers that she was due to give birth on March 1, the birthday of Robin's late father Alan Thicke.