The baby boy is the royal couple's third child [Photo: Courtesy]

Proud parents the Duke and Duchess of Cambridge smiled broadly as they introduced their third child to the world yesterday.

Wills, 35, and Kate, 36, emerged from hospital at 6pm - just seven hours after the birth at 11.01am.

The baby boy – weighing 8lb 7oz – is fifth in line to the throne, knocking Prince Harry down to sixth.

Born on St George’s Day, the tot is the Queen’s sixth great-grandchild.

Kate beamed as she cradled the baby in her arms and walked down the steps of the private Lindo Wing of St Mary’s Hospital, in Paddington, West London, as a huge cheer went up from the crowds.

The couple's third child was born on Monday [Photo: Courtesy]

A professional lip reader has revealed this is what the couple said.

William : Are you OK with him?

Kate : Yeah.

William : Look, there he is. Over there. [They wave to the left]

Kate : Let’s just wave over there. [They wave to the right]

Kate : Look, he is there. [They wave] It is a bit windy, eh? He might get cold. Let’s go now.

William : Sure

Wearing a bright red dress by British designer Jenny Packham – the same designer she chose when she left hospital with George and Charlotte – Kate waved and looked up at the staff and patients peering out of the hospital buildings above.

The royal baby [Photo: Courtesy]

The frock bore a resemblance to what Diana wore when she and Charles emerged from the Lindo Wing with new-born Prince Harry in 1984.

As the royal couple prepared to drive away from hospital with their new-born son, William joked about having his hands full

The Duke held up three fingers to well-wishers, said “thrice worry now” and smiled warmly.

The baby’s name was not revealed yesterday but William said “you’ll find out soon” when asked what they planned to call him.

He added the family are “delighted” about the new arrival and the new-born’s brother George, four, and sister Charlotte, two, are “very happy”.

Wills also joked about the departure from hospital, saying: “We didn’t keep you waiting too long this time.”