The Queen is "delighted" after the Duke and Duchess of Sussex announced the birth of their second child, Lilibet "Lili" Diana Mountbatten-Windsor, Buckingham Palace has said.
The Prince of Wales and the Duke of Cambridge also congratulated the couple on social media.
The Queen's 11th great-grandchild was born on Friday at a hospital in Santa Barbara, California.
Lilibet was the Queen's nickname when she was a child.
Buckingham Palace said: "The Queen, the Prince of Wales and the Duchess of Cornwall, and the Duke and Duchess of Cambridge have been informed and are delighted with the news."
Prince Charles, Prince Harry's father, and the Duchess of Cornwall tweeted: "Congratulations to Harry, Meghan and Archie on the arrival of baby Lilibet Diana. Wishing them all well at this special time."