Three times the worry! That was the reaction of delighted dad Prince William as he proudly showed off his third child to crowds eagerly awaiting the arrival of a new St George's Day royal baby.

Eastern Daily Press: The Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: Aaron Chown/PA WireThe Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: Aaron Chown/PA Wire

On the most patriotic day of the year, royal watchers gathered outside St Mary's Hospital in London from early in the morning after the Duchess of Cambridge was admitted before 6am.

She gave birth to the 8lb 7oz baby boy at 11.01am, later bringing the as yet un-named prince out onto the steps of the Lindo Wing to show off to the world.

During his first photocall, the baby - a younger brother to Prince George and Princess Charlotte - was carried in his mother's arms wrapped in a white lace shawl with a matching hat.

Smiling broadly, Kate - dressed in a vibrant red Jenny Packham dress with a white lace collar - adjusted the baby's shawl amid windy conditions outside the hospital.

Eastern Daily Press: The Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: Dominic Lipinski/PA WireThe Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: Dominic Lipinski/PA Wire

The baby could be seen moving his fingers as he was cradled by Kate.

Minutes after the brief photocall, the couple headed home to the sanctuary of Kensington Palace, with William emerging from the hospital carrying his son in a car seat, and holding Kate's hand.

The Duke said they were 'very happy' and 'very delighted' and joked, holding up three fingers, that he now had 'thrice the worry now'.

He added: 'We didn't keep you waiting too long this time.'

Eastern Daily Press: The Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: Dominic Lipinski/PA WireThe Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: Dominic Lipinski/PA Wire

Quizzed on whether they had decided on a name, the Duke added: 'You'll find out soon enough.'

George and Charlotte earlier met the newest addition to the Cambridge family after being brought to St Mary's Hospital by William.

A confident Charlotte, who turns three on May 2, turned to wave at the photographers as she led the way up the steps holding the Duke's hand, while four-year-old George appeared more wary of the huge crowds of media.

William and Kate thanked the hospital for their care and the public for their warm wishes.

Eastern Daily Press: The Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: David Mirzoeff/PA WireThe Duke and Duchess of Cambridge and their newborn son outside the Lindo Wing at St Mary's Hospital in Paddington, London. Picture: David Mirzoeff/PA Wire

Kensington Palace said: 'Their Royal Highnesses would like to thank all staff at the hospital for the care and treatment they have received.

'They would also like to thank everyone for their warm wishes.'