Royal baby: Politicians and celebrities from David Cameron to Kim Kardashian send congratulations to Will and Kate

Crowds have gathered in front of Buckingham Palace, while others have taken to Twitter to send their good wishes (AP)

Twitter exploded with messages of congratulations for the Royal couple following the announcement that Kate had finally given birth to a boy this afternoon.

The meltdown came after more than a week of daily rumours had circulated on the social networking site that the Duchess had already gone into labour.

When the official announcement of the birth finally came, politicians, celebrities and well-wishers across the world rushed to congratulate Prince William and new mother Kate.

Among the first to take to Twitter were the leaders of the three main political parties.

David Cameron tweeted: “I’m delighted for the Duke and Duchess now their son has been born. The whole country will celebrate. They’ll make wonderful parents.”

Ed Miliband added: “Many congratulations to the Duke and Duchess of Cambridge. I wish them and their son all happiness and good health.”

And Nick Clegg said: “Congratulations to The Duke and Duchess of Cambridge. Good news to make the whole country smile.”

Broadcaster Piers Morgan tweeted: "Keep Calm...and Carry On. Kate" and added: "My money's on an Australian cricket birth - all out by tea."

He also told one of his followers Prince William’s late mother Princess Dianna would have "loved" the news her son’s first child was on the way.

The Archbishop of Canterbury, the Most Rev Justin Welby, also tweeted: "My thoughts and prayers are with Kate and the whole family on this enormously special day."

And Labour's former deputy prime minister John Prescott joked: "Great to hear the Duchess of Cambridge has gone into labour. Is she an affiliated member?"

Former Spice Girl and America's Got Talent judge Mel Brown was another of the many who took to Twitter, posting: "Whoop whoop, the royal baby is coming."

US celebrities also sent messages to the happy couple, with veteran actor William Shatner tweeting “So pleased to hear that William and Kate had a baby boy. Long live the future king. MBB.”

Meanwhile, talkshow host and comedian Ellen DeGeneres quipped: “How can you tell when there's about to be a royal baby? When they start crowning. I'll be here all week.”

A Prince is born: The Twitter response

David Cameron ‏@David_Cameron1h

I'm delighted for the Duke and Duchess now their son has been born. The whole country will celebrate. They'll make wonderful parents.

Ed Miliband ‏@Ed_Miliband1h

Many congratulations to the Duke and Duchess of Cambridge. I wish them and their son all happiness and good health.

Nick Clegg ‏@nick_clegg49m

Congratulations to The Duke and Duchess of Cambridge. Good news to make the whole country smile

Ellen DeGeneres ‏@TheEllenShow3h

How can you tell when there's about to be a royal baby? When they start crowning. I'll be here all week.

Dan Wootton ‏@danwootton7m

“@theroyaleditor: Royal doctor Marcus Setchell says "wonderful baby. Beautiful baby".”

Bill Neely ‏@billneelyitv9m

The lovely Arthur Edwards, Royal photographer , says Kate is likely to leave hospital with baby tomorrow. Listen 2 the wise man. #RoyalBaby

No. 10 Press Office ‏@Number10press15m

PM on #RoyalBaby: An important moment for our nation but above all a wonderful moment for a warm and loving couple.

Ed Balls ‏@edballsmp16m

Fabulous news on the birth of the Royal baby boy - such an exciting day for any couple - now looking forward to the name..

Justin Welby ‏@ABCJustin1h

Delighted for the Duke and Duchess of Cambridge as they welcome their baby boy. May God bless them all with love, health and happiness.

John Prescott ‏@johnprescott14h

Great to hear the Duchess of Cambridge has gone into labour. Is she an affiliated member? #boomtish #royalbaby

Sadiq Khan MP ‏@SadiqKhan20m

1/2 #RoyalBaby clearly only news in town. Congrats to Wills & Kate & to all those parents celebrating new arrivals today.

Kim Kardashian ‏@KimKardashearn30m

Kate Middleton's Baby, congratulations! :)

Louise Mensch ‏@LouiseMensch36m

My name is Prince. And I am funky #RoyalBaby

Melanie Brown ‏@OfficialMelB13h

Whoop whoop the royal baby is comming

William Shatner So pleased to hear that William and Kate had a baby boy. Long live the future king. MBB

Jack Osbourne

EPIC!!!! a new prince was born. its like real life Game of Thrones #royalbaby