It's a "healthy" baby boy for Prince Harry and wife Meghan Markle, making him seventh-in-line to the British throne.
The 34-year-old father, Duke of Sussex, was present at the birth of his boy, who weighs 3.2 kg.
The new father, Prince Harry, told reporters that Meghan and the baby were doing "incredibly well" and that the couple were "absolutely thrilled" since the birth at 0526 am (local time).
"It's been the most amazing experience I can ever possibly imagine. How any woman does what they do is beyond comprehension,” said Prince Harry, making a brief media appearance as a new father.
"It was amazing, absolutely incredible. I'm so incredibly proud of my wife and as every father would say, this baby is absolutely to die for… So, I'm just over the moon," he said, confirming that the baby was "a little bit overdue" and that the couple were still deciding on a name.
"The couple thank members of the public for their shared excitement and support during this very special time in their lives," the palace said, adding that, "More details will be shared in the forthcoming days." Meghan, 37, went into labour "in the early hours" of Monday morning.
The new royal baby, as Queen Elizabeth II's eighth great grandchild, will be seventh-in-line to the British throne.
He or she will be in line behind its grandfather Prince Charles, uncle Prince William and his children – Prince George, Princess Charlotte and Prince Louis – and father Harry, Duke of Sussex.
However, the baby will not be bestowed a title of His or Her Royal Highness (HRH), or referred to as a Prince or Princess, unless the 93-year-old monarch steps in to make an exception to the royal titles rule dating back to 1917.
The boy will be able to use one of Harry's lesser titles to be known as the Earl of Dumbarton.
Meghan, a former actress, and Harry got married at a lavish wedding ceremony in Windsor Castle in May last year and announced the pregnancy publicly in October 2018, on the first day of their Commonwealth tour of Australia and New Zealand.
In a break from usual royal tradition, the couple have chosen to keep the birthing plans for their baby a private affair and said that they would be announcing the birth publicly only "once they have a chance to celebrate privately as a family".
The Duke and Duchess of Sussex had moved out of their London home at Nottingham Cottage in Kensington Palace into their newly-refurbished 10-bedroom family home at Frogmore Cottage in Windsor on the Queen's estate recently in preparation of the new arrival.
Their new home has a curious Indian history as the cottage which was a royal gift to Abdul Karim by Queen Victoria, then Empress of India, in recognition of his service and as a sign of her affection towards her Indian aide and confidant.
Harry and Meghan, who have been based at Frogmore Cottage since early April, were appointed Youth Ambassadors for the Commonwealth by the Queen and there have been some speculative UK media reports on them choosing to be based in Africa as part of that role in the future.