Robin Thicke Expecting Second Child With Girlfriend April Love Geary

Robin Thicke and April Love Geary have a bun in the oven — again.

The singer and his girlfriend shared on Instagram Tuesday that they are expecting their second child together, six months after welcoming their first.

"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! 😇" she captioned a video of their 6-month-old daughter Mia Love holding the sonogram.

"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! 😝" she continued.

In the Instagram video, PEOPLE first reported, Geary asks Mia, "What are you holding? is that your little baby brother or sister? What do you think? Are you excited?"

Thicke is also father to 8-year-old son Julian Fuego from his marriage to actress Paula Patton.

Thick and Geary started dating following his separation from Patton in February 2014.

Patton filed for divorce in October 2014 and in March 2015, their divorce was finalized. That same year, the former couple was embroiled in a lengthy custody dispute, which was resolved.

Thicke and Geary made their first public appearance together at the Cannes Film Festival in May 2015 after dating for over a year.

The pair frequently posts about their romance and their baby girl on social media and she previously joked about the couple's 18-year-age gap in April 2017.

Mia was born on Feb. 22 via a scheduled C-Section. Thicke also posted a video of himself cradling the newborn, with her face away from the camera, to celebrate the happy news. "On 2/22 at 13:33 Mia Love Thicke was born. Thank you God and April Love," the "Blurred Lines" singer wrote on Instagram.

The couple have not tied the knot yet. In November 2016, there were rumors they were on their honeymoon after they poste their latest PDA-filled, sun-bleached photos. They even got each others' initials tattooed on their fingers to celebrate their second anniversary together. However, a source told PEOPLE at the time that they were just dating.

Since the arrival of their baby girl, Geary has been open about breastfeeding, not afraid to call out critics.

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"Maybe the next time you want to criticize me for posting a picture of myself breastfeeding you should really take a look at the pictures you've had taken," Geary wrote on Instagram. "Not that taking nudes are wrong! The naked body is a beautiful thing! But don't be a hypocrite mama."

Thicke also has not released a new album since 2014's Paula, which was dedicated to Patton. He has released four singles since then, including "Morning Sun" and "Back Together," but none have surfaced on an album.