"Many congratulations to the Duke and Duchess of Cambridge," the Prime Minister tweeted on Monday, minutes after the official announcement was made by Clarence House. "I'm delighted by the happy news they they're expecting another baby."
William and Kate's baby news has been welcomed by the country – and the rest of the world.
In a statement, Clarence House said that the Queen and members of both families were "delighted" that the couple are expecting their second child together.
Deputy Prime Minister Nick Clegg and Labour leader Ed Milliband have also offered their well-wishes, the latter tweeting, "Fantastic to hear that Prince George will soon be a big brother! Congratulations to the Duke and Duchess of Cambridge on their happy news."
The Archbishop of Canterbury Justin Welby, meanwhile, wrote, "Wonderful news that the Duke & Duchess of Cambridge are expecting second child.
"Praying for the family, and that the morning sickness subsides," following the confirmation that Kate is once again suffering with Hyperemesis Gravidarum, and is currently being treated by doctors at Kensington Palace.
Among the other offering their congratulations to the royal couple, who celebrated Prince George's first birthday in July, was Giovanna Fletcher, who tweeted, "Yay! Another royal baby! Hurrah! #KateandWills #RoyalBaby."