Hallo royal baby!

With the arrival of a new prince at 11.01am on Monday - the third child for the Duke and Duchess of Cambridge - Britain has been celebrating.

Prince William was bursting with pride, his wife Kate clearly besotted. And the third Cambridge baby? Fast asleep, but seemingly secure of his new place in the world.

The newborn prince signalled his arrival with three tiny fingers as he made his public debut, fast asleep in the arms of his mother.

And while his newborn son was oblivious to the excitement he had caused, the Duke embarked on his new life with three children with no illusions, holding up three fingers and joking his enlarged brood would give him “thrice worry now“.

The baby prince, a younger brother to Prince George and Princess Charlotte, was born at 11.01am yesterday (Monday), weighing 8lb 7oz. The newborn, whose name had last night not yet been announced, was lulled to sleep in his mother’s arms as cooed “hello” and wrapped him up closely against the cold wind.

The Duke and Duchess, rarely anything less than poised, appeared old hands at parenting, walking down the steps of the Lindo Wing a mere seven hours after their son was born to greet well-wishers.

Prince George and Princess Charlotte, the stars of the show as they marched up to the hospital for a visit, were “very happy” to meet their little brother, the Duke, said, proclaiming the young family “delighted“. As a nervous George held his father’s hand, Charlotte marched proudly along the street outside the hospital, waving to the cameras and turning at the last second as she climbed the stairs to the door to unwittingly ensure they caught her beaming smile.

Yesterday, the Duke and Duchess were kept busy settling in to life as a family of five at Kensington Palace, Prince George and Princess Charlotte already having been introduced to their brother at St Mary’s Hospital.

Pippa Matthews, the first visitor seen driving into the palace yesterday, spent several hours with her sister, the Duchess, and infant nephew before driving away.

Carole and Michael Middleton, the Duchess’s parents, were unlikely to have been far away.

Prince Harry and Meghan Markle, too, could surely not have kept away from joining the first eager visitors, living just next door and both adoring children. The Prince once called George and Charlotte “the most amazing things ever".

The Queen, who was in Windsor, is unlikely to meet her sixth great-grandchild imminently, with further duties at the castle today, while the Duke of Edinburgh is recuperating privately from a hip replacement operation.

The baby’s name will be shared first with the Queen before being announced to the public, with family members remaining tight-lipped about the final decision.

The Countess of Wessex, who was conducting a string of -engagements near Truro, Cornwall, said: “I’m thrilled for them all, it’s lovely — really good news.”

Asked about the baby’s name, she added tactfully: “I don’t know, we’re all just going to have to wait and see.”

Official celebrations were already under way, with the bells of Westminster Abbey ringing out from 1pm and gun salutes fired in London at 2pm.

The King’s Troop Royal Horse Artillery rode out from Wellington Barracks into Hyde Park for a 41-round salute, and the Honourable Artillery Company (HAC), the City of London’s Army Reserve regiment, fired a 62-round gun salute from the Tower of London.

Like any doting grandfather, Prince Charles - the heir to the throne of England - could not have been happier at the safe arrival of his new baby grandson. Like any man nearing 70, the combined energy of three children under five gave him a little light-hearted pause for thought.

The Prince of Wales is now a grandfather to Prince George, four, Princess Charlotte, who will turn three on May 2, and the as-yet-unnamed baby boy.

The Duchess of Cornwall also has five grandchildren who are regular visitors to their home.

The Prince’s words chimed perfectly with those of his son the Duke, who had held up three fingers — one for each of his children — when departing from hospital and laughed that he had “thrice the worry now".

Warm wishes were shared by political leaders, Royal admirers and family friends.

Former US first lady -Michelle Obama, who famously met Prince George at Kensington Palace in his dressing gown during a presidential visit, said: “Barack and I are thrilled to congratulate the Duke and Duchess of Cambridge on their newest arrival! We hope to meet him soon for a Kensington Palace pyjama party. I’ll wear my robe!“

Niagara Falls, in Canada, was turned blue in honour of the newborn Prince.

The baby joy extended not just to the Royal Family and avid monarchists.

Tyler O’Hare, a young Metropolitan Police constable who took centre stage as the “door officer” during the royal baby’s first public appearance outside the Lindo Wing of St Mary’s described the honour as “amazing” and “a highlight of my career“, on Twitter.

The Duke and Duchess of Cambridge are expected to share the name of their third baby — born at 11.01am on Monday, weighing 3.8kg — today, and are also likely to thank well-wishers. -The Daily Telegraph