An "overjoyed" Duke and Duchess of Sussex are expecting a baby, with a spokesperson for the couple confirming the pregnancy on Valentine's Day.

Prince Harry and Meghan Markle will welcome a brother or sister for son Archie Mountbatten-Windsor, who turns two in May.

"We can confirm that Archie is going to be a big brother," a spokesperson said.

"The Duke and Duchess of Sussex are overjoyed to be expecting their second child."

Watch: Meghan and Harry. Post continues below video.

A Buckingham Palace spokesman said the Queen and Prince Philip and the entire royal family were delighted by the news and wished the couple well.

It comes after Meghan wrote about having a miscarriage last year in a deeply personal article for the New York Times, writing: "I knew, as I clutched my firstborn child, that I was losing my second."

Harry, 36, and Meghan, 39, quit their roles as senior working royals in March 2020 in a quest for personal and financial freedom, and now live in California.

The Valentine's Day announcement came just five days after the royal family celebrated the arrival of Princess Eugenie's first child, a boy.

Baby Sussex will be the Queen and the Duke of Edinburgh's 10th or 11th great-grandchild depending on whether he or she arrives before or after Zara Tindall's baby, which is also due in 2021.

The new baby will still be eighth in line to the throne and the Prince of Wales's fifth grandchild.

Photographer Misan Harriman.

The couple shared a black-and-white photo of themselves under a tree with Harry resting his hand on Meghan's head as she lies in his lap cradling her bump.

The photograph shared was taken virtually by photographer Misan Harriman on an iPad.

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

Harriman is a close friend of the Duke and Duchess and was a guest at their 2018 wedding. 

He is a Nigerian-born British photographer, entrepreneur and social activist, who became one of the most widely-shared photographers of the Black Lives Matter movement in 2020. He's also the first black man to shoot a cover of British Vogue and was the photographer who shot photos for Princess Beatrice's engagement to Edoardo Mapellli Mozzi in September 2019.

The Valentine's Day announcement.

The front page of Britain's newspapers were covered in happy news on Valentine's Day, 1984, as the night before, the royal family had announced Princess Diana was expecting her and Prince Charles' second child - the future Prince Harry.

A touching tribute announcing for the Sussexes to announce their exciting news on #ValentinesDay❤️ It was exactly 37 years ago that Princess Diana shared with the world that she was pregnant with Prince Harry. pic.twitter.com/NQfUiw62Sc

— Omid Scobie (@scobie) February 14, 2021

Now Harry and Meghan have announced Meghan's pregnant with their second child 37 years later. Plus, Valentine's Day is a pretty iconic day for these major milestones.

The dress.

The photo of the Duke and Duchess of Sussex is pretty casual, especially by royal standards. Meghan is wearing a custom made Carolina Herrera dress, which was made for her while she was pregnant with Archie.

Meghan has a longtime relationship with the brand's creative director, Wes Gordon.

When is Meghan due?

The Sussexes did not provide any information about the sex or specific due date of their baby, similar to how they introduced Archie's pregnancy too.

Typically, pregnancies are announced after the first trimester, but it is thought the Duchess could be around the five-month mark. Since we don't know for sure, we can't exactly nail down the date beyond that she's likely to give birth during the Northern Hemisphere summer.

Image: Getty. 

The baby announcement comes not long after Meghan's moving essay for the New York Times in which she shared that she'd suffered a miscarriage in July 2020.

"Losing a child means carrying an almost unbearable grief, experienced by many but talked about by few. In the pain of our loss, my husband and I discovered that in a room of 100 women, 10 to 20 of them will have suffered from miscarriage. Yet despite the staggering commonality of this pain, the conversation remains taboo, riddled with (unwarranted) shame, and perpetuating a cycle of solitary mourning," she wrote.