For most couples, the arrival of a third child means last minute packing of a hospital bag and a quick trip in and out of hospital without much of a fuss.

But for the Duke and Duchess of Cambridge, the birth of their third child was greeted with just as much fanfare as the first, with fanatic royalists camping outside the hospital for weeks, flags being raised across the country and the official birth announcement going on display on an ornate golden easel.

Kensington Palace announced the arrival of the new prince on Monday, saying Kate was "delivered" of a son, weighing 8lbs 7oz, at 11.01am.

READ MORE: New prince tipped to be named Arthur

The statement added: "Her Royal Highness and her child are both doing well."

Outside the exclusive Lindo Wing of St Mary’s Hospital in Paddington, self-appointed town crier Tony Appleton announced the news to the waiting crowd and media pack eager to hear if it was a boy or a girl.

Royal fans dressed head-to-toe in union flags and cuddling their own royal baby dolls cheered and hugged in celebration.

Many of them have slept outside the hospital for several nights to secure a prime spot to catch a first glimpse of the new arrival, who is fifth in line to the throne.

Royalists Maria Scott, 46, from Newcastle, John Loughrey, 63, from Streatham, and Terry Hutt, 83, from Weston-Super-Mare, have been camped outside the hospital for the past two weeks.

READ MORE: New prince tipped to be named Arthur

Waving banners welcoming a new prince or princess, the superfans - who have been at the birth of all three babies - said the timing of the announcement, falling on St George's Day, added to the occasion.

Mr Loughrey said: "We are so pleased. We have been here for 15 days.

"I'm so pleased it's St George's Day. St George himself would be very pleased if the baby's born today.

"It's very good for our country and of course Her Majesty the Queen."

Speaking from outside a make-shift camp with royal memorabilia and a union flag tent, Mr Hutt added that it was "fantastic to have another newborn baby".

Another superfan Margaret Tyler, who is regularly spotted at royal family events, told how she did not wait it out too long this time round.

The 74-year-old, possibly Britain's largest collector of royal memorabilia, said: ""I waited for George for six days and Charlotte for 11 but today I just timed spot on.

"I couldn't have been waiting here for days and days as I was outside the palace to celebrate Her Majesty's 92nd birthday.

"It's very exciting to be here and an incredible moment.

"This is such an exciting year for the Royals and I'm already preparing to be in Windsor next month [for the wedding of Prince Harry and Meghan Markle]."

READ MORE: New prince tipped to be named Arthur

Congratulations have poured in for William and Kate, with St Andrews University, where the couple met, one of the first to tweet about the news, saying: "Baby joy for Fife graduates - #congrats to Catherine Middleton, art history Class of 2005 & William Wales, geography Class of 2005, on the birth of their 3rd child. #RoyalBaby."

Prime Minister Theresa May also tweeted her "warmest congratulations" and wished them "great happiness for the future".

Others made light of the new arrival, with comedian David Walliams quipping on Twitter: “Prince Harry just got demoted again.”

Scottish author JK Rowling also reacted to a reporter saying that "Prince Harry’s route to the throne just became more difficult".

She tweeted that it was "as though it's an open secret he’s planning to systematically slaughter his closest relatives".

The name of the new arrival has yet to be confirmed, but Arthur, Albert and Philip all tipped as strong contenders.

However, a few other suggestions also appeared on social media, with David Walliams suggesting it would be "Kanye", while Crystal Palace Football Club suggested the new arrival's name was "Palace".