A statement from Buckingham Palace said: "Her Majesty, the Duke of Edinburgh, Prince of Wales and the entire royal family are delighted and wish them well."
The news was released on Sunday night, Valentine's Day, via representatives for the royal couple.
A spokesperson for the Duke and Duchess told the press: "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."
WATCH: Baby number two is on the way for Prince Harry and Meghan
The news was accompanied by a gorgeous black-and-white photo of the pair showing Meghan with her head in Harry's lap as she cradles her baby bump.
The shot was taken remotely by photographer and friend of the couple Misan Harriman.
The couple released a romantic photo to mark their happy news
In the picture, the Duchess is wearing a long dress by Carolina Herrera, which she also wore during her pregnancy with Archie.
Sweetly, the news echoes Princess Diana's announcement of her pregnancy with Prince Harry, on Valentine's Day back in 1984.
It also comes just a few days after the royal family celebrated the arrival of the Queen and Prince Philip's latest grandchild.
Following the happy news that Princess Eugenie and her husband Jack Brooksbank had welcomed her first child, a baby boy, an official statement was released by Buckingham Palace.
The Duke and Duchess welcomed baby Archie in May 2019
It read: "The Queen, The Duke of Edinburgh, The Duke of York, Sarah, Duchess of York, and Mr and Mrs George Brooksbank are delighted with the news.
"This is Princess Eugenie and Jack Brooksbank's first child, The Duke of York and Sarah, Duchess of York's first grandchild, and the ninth great-grandchild for the Queen and The Duke of Edinburgh."
Princess Eugenie, 30, and Jack, 34, confirmed the birth of their baby on 9 February. The little boy is currently 11th in line to the throne.
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