The celebrity couple, who relocated to Santa Barbara, California, last year, announced the news via a spokesperson on Valentine's Day.
They also shared a romantic black and white pic of themselves taken by one of Meghan's childhood friends, photographer Misan Harriman.
Prince Harry and Meghan Markle announce new arrival
Misan posted the pic on his Twitter page, along with a heartwarming message to the pair.
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!#remoteshoot #shotonipad #shotbymisan pic.twitter.com/3iSYjydVj9— Misan Harriman (@misanharriman) February 14, 2021
The news means Harry and Meghan will soon have four little ones to take care of. They've currently got their paws full with baby Archie, who turns two later this year, and their fur babies Guy and Pula.
And just to make sure that nobody forgets about them, the cheeky pair recently gatecrashed a filmed talk between Meghan and journalist Gloria Marie Steinem. Meghan and Gloria were discussing issues about voting and women's rights when the furry duo decided they wanted some of the limelight.
Meghan Markle is a super celebrity dog mum
But like every good dog mum, Meghan saw the funny side. She even managed to dish out a few belly rubs during the interview.
Meghan is well known for her love of dogs. She sits on the board of canine rescue service Mayhew and recently praised dogs for the way they're helping so many owners through lockdown.
See also: Meghan Markle wants to adopt another dog to help shelter during virus outbreak