Celebrities and politicians have been sending their best wishes to the Duke and Duchess of Cambridge on social media.
Prime Minister Theresa May sent her "warmest congratulations to the Duke and Duchess of Cambridge on the birth of their baby boy".
"I wish them great happiness for the future," she added.
Mayor of London Sadiq Khan tweeted: "On behalf of Londoners, I want to send our warmest congratulations to the Duke & Duchess of Cambridge on the birth of their baby boy."
Foreign Secretary Boris Johnson and Shadow Home Secretary Diane Abbott also sent their congratulations as politicians from across the political spectrum reacted with joy to the news of a new royal baby.
Mr Johnson offered his "huge congratulations to Their Royal Highnesses The Duke and Duchess of Cambridge on the safe delivery of their baby boy!"
Former world heavyweight champion boxer, Frank Bruno MBE, Hollywood actress Mia Farrow and TV presenter Paddy McGuiness were among the celebrity well wishers on social media.
Meanwhile, comedian David Walliams quipped: "Prince Harry just got demoted again."