The news spread like wildfire that the Duchess had given birth to a little Prince weighing 8lb 6oz at 4:24pm on Monday afternoon.
As the nation's celebrations kicked off, celebrities took to the site to congratulate the new parents and share their excitement at the happy news. HELLO! Online takes a look at the top celebrity tweets:
Twitter messages for William and Kate
Cheryl Cole: Congratulations to William and Kate!! So happy they have a healthy baby and everyone is good. Can't wait to see him now 👶 #Royalbaby
Ellen DeGeneres: It's a boy! So happy for my cousin Kate and the future King of England!
Emma Bunton: It's a boy!!! Special times ahead for Kate and William. Xxxx
Katherine Jenkins: Awwww... It's a boy! Congratulations! Sooo happy for you! #GlassesRaised #Toast #Celebrations
Cara Delevingne: It's a boy!!! Congratulations William and Kate!! X
Amanda Holden: Congratulations to William and Kate. WONDERFUL NEWS! A little Prince
Joan Rivers Congratulations to Kate & William on the birth of their baby boy! So relieved that his name won’t include the words Ivy or Apple.
Millie Mackintosh I knew it was going to be a boy! #royalbaby
Rochelle Humes:A future King...a little baby boy. How exciting x
Pixie Lott: Congratulations Kate and William! The most lovely news <3
Kimberley Walsh:Aaarrgghh it's a boy!!!!!!!!!!!!!!#RoyalBaby
Jack Osbourne:EPIC!!!! a new prince was born. its like real life Game of Thrones #royalbaby
Marvin Humes:Congratulations to William and Kate! There's no better feeling than the arrival of your child! Great news!
Vernon Kay:Congratulations William and Kate:-) See you at Jungle mania,summer camp, Legoland,kids club and ToysRUs very soon.X