Meghan Markle and Prince Harry have another bun in the oven ... they're expecting baby #2.

The Duke and Duchess of Sussex made the announcement Sunday, saying they are due to have a second child together ... although they didn't reveal how far along Meghan is, or the sex of the baby.

The couple says, "We can confirm that Archie is going to be a big brother. The Duke and Duchess of Sussex are overjoyed to be expecting their second child." It looks like they already posed for some maternity shots too -- photo and personal friend Misan Harriman snapped some photos of Meghan and Harry in a lush forest, showing off her baby bump.

Harriman apparently did the photoshoot remotely, adding this ... "Meg, I was there at your wedding to witness this love story begin, and my friend, I am honoured to capture it grow. Congratulations to The Duke and Duchess of Sussex on this joyous news!"

The news comes not too long after Meghan revealed in November she'd suffered a miscarriage this past July, detailing the heartache and agony she and Harry went through ... and in private, no less. Her pregnancy wasn't known until she discussed it in the NYT.

Archie, who was born in 2019, will be turning 2 in May. Not a bad age difference as an older sibling.

Congrats!!!