Prince Harry and wife Meghan have named their child Archie Harrison Mountbatten-Windsor.
The name is believed to have little precedent within the modern British royal family.
The couple shared the news on Instagram with an image of Queen Elizabeth and the Duke of Edinburgh meeting their newest great-grandchild.
Newly parents made their son’s appearance in public on Wednesday.
The newest royal baby, wrapped in a white blanket and wearing a matching cap, appeared at full ease and apparently sleeping as dad Prince Harry cradled him in his arms, posing for the shutterbugs who had been waiting impatiently to click “Baby Sussex”.
Many believe Meghan, the Duchess of Sussex, chose the name that reflects her American heritage.
Before giving him an official name, the infant was known only as Baby Sussex when he was born on early Monday morning.
According to Meghan, “the baby has the sweetest temperament and he’s really calm. He’s been a dream”.
Grandfather Prince Charles, who is on an official visit to Germany with the Duchess of Cornwall Camilla, said, “We couldn’t be more delighted at the news and we’re looking forward to meeting the baby when we return.”
Baby Archie’s maternal grandmother, Meghan’s mother Doria Ragland, is “overjoyed at the arrival of her first grandchild”. She was with Meghan at Frogmore Cottage – the new parents’ home on the Windsor Estate.