A delighted Prince Harry has spoken of his joy at being a dad and his pride in his "incredible wife".
Speaking from Windsor, the Duke of Sussex said: "I'm very excited to announce that Meghan and myself had a baby boy this morning, a very healthy baby boy...Mother and baby are doing incredibly well."
He said: "It's been the most amazing experience. We are both absolutely thrilled and grateful to the support from everybody out there."
Prince Harry said they were still thinking about names but would show off their baby in the two days' time.
The Duke of Sussex added: "It's absolutely incredible and I'm so incredibly proud of my wife."
Harry, who was present for the birth, said his son was "absolutely to die for...I'm absolutely over the moon".
The birth was announced, as expected, on the couple's new Instagram page. A formal announcement followed soon after.
"Her Royal Highness The Duchess of Sussex was safely delivered of a son at 0526hrs (2.26pm Monday AEST)," Buckingham Palace said in a statement. "The baby weighs 7lbs 3oz (3.26kg).
"The Duke of Sussex was present for the birth."
The statement continued: "The Duchess and baby are both healthy and well, and the couple thank members of the public for their shared excitement and support during this very special time in their lives.
More details will be shared in the forthcoming days," they posted on Instagram.
Meghan's mum Doria Ragland was by her side during the birth, having flown in to the UK from Los Angeles late last month.