The prince is the couple's third child, following their eldest Prince George and Princess Charlotte.
Fans across the globe were overjoyed when the Palace tweeted the huge news, announcing to the world:
"Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs."
Revealing, "The baby weighs 8lbs 7oz [about 3.8kgs]."
And new-dad-of-three Prince William was also there, with the palace sharing, "The Duke of Cambridge was present for the birth."
"Her Royal Highness and her child are both doing well."
The Palace released details of the birth, confirming the medical staff in support were:
- Mr. Guy Thorpe-Beeston, Surgeon Gynaecologist to The Royal Household
- Mr. Alan Farthing, Surgeon Gynaecologist to Her Majesty The Queen
- Dr. Sunit Godambe, Consultant Neonatologist at Imperial College NHS Trust
- Professor Huw Thomas, Physician to Her Majesty The Queen and Head of the Medical Household
Kate and Will's third child is fifth in the line of Succession after His Royal Highness The Prince of Wales, His Royal Highness The Duke of Cambridge, His Royal Highness Prince George of Cambridge and Her Royal Highness Princess Charlotte of Cambridge.
He is styled His Royal Highness Prince [name] of Cambridge.
Kensington Palace confirmed the Duchess was in labour at 08:23am in the morning, London time via Twitter in a statement which read: "Her Royal Highness The Duchess of Cambridge was admitted to St. Mary's Hospital, Paddington, London earlier this morning in the early stages of labour."
"The Duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital with The Duke of Cambridge."
No doubt Nanny Maria Bello will have Princess Charlotte and Prince George on their way to Lindo Wing at St Mary's Hospital in Paddington to meet the newest Cambridge sibling imminently.
Royals, fans and celebrities have been quick to share their congratulations to Prince William and Duchess Catherine for their new son.
Kensington Palace shared, "The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news."