The royal couple welcomed a son into the world at 11.01am on Monday (23.04.18), and they've been flooded with patriotic messages from the showbiz world since.
Among the first to comment on their new arrival was One Direction star Liam, who performed for the royals - including Prince Harry and Meghan Markle - at a Commonwealth Day service at Westminster Abbey last month.
Taking to Twitter, Liam wrote: ''Congratulations to her Royal Highness the Duchess of Cambridge Kate and the Duke of Cambridge, Prince William on the birth of their baby boy! #RoyalBaby (sic)''
The 24-year-old singer's partner Cheryl - with whom he has 13-month-old son Bear - was one of the first to congratulate the couple when they announced they were set to add to their brood - which also includes Prince George, four, and Princess Charlotte, two - in September.
Comedienne Sarah Silverman took bets on witty names they could name the future heir, writing: ''Royal baby name pitches: Joseph, Michael, Henry, Idris, Sandy, Clyde, Butch, Grandpa Al Lewis, Jude, Bub (sic)''
And referring to the royal Netflix series 'The Crown', US TV host Ellen Degeneres wrote: ''It's a boy! Kate Middleton's new baby is now 5th in line to the throne, and season 43 of 'The Crown' (sic)''
Former The Wanted star Nathan Sykes revealed he was thrilled to hear the news.
He said: ''I do get rather excited when everyone is excited about a #royalbaby (sic)''
'Britain's Got Talent' host David Walliams joked that the 35-year-old prince and his 36-year-old wife should name their child after rapper Kanye West.
He quipped on Twitter: ''BREAKING NEWS. New #royalbaby name is 'Kanye'. (sic)''
Actress Elizabeth Banks wrote: ''I love #royalbabies #royalbaby3 congrats to all of us but mostly to the parents and big sibs (sic)''
Announcing the arrival on Monday (23.04.18), Kensington Palace announced: ''Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs.
''The baby weighs 8lbs 7oz.
''The Duke of Cambridge was present for the birth.
''Her Royal Highness and her child are both doing well.''
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