Kate Middleton has given birth to a baby boy weighing 8 lb 6 oz at St Mary's Hospital in London with Prince William by her bedside.
The baby was born at around 4.24pm, and news of the birth was officially broken around four hours later via a statement from Kensington Palace, which confirmed that mother and baby are doing well.
Shortly afterwards Ed Perkins, head of news at the Royal Household, emerged from the hospital carrying a medical bulletin confirming the birth of a baby boy. The bulletin was signed by the Queen's former gynaecologist, Marcus Setchell, leader of the team which oversaw the birth.
In keeping with tradition, a bulletin relaying news of the birth was also posted on an easel outside Buckingham Palace. The document was placed by a Buckingham Palace official, accompanied by a footman.
The Queen was the first person outside the hospital to be informed of the birth. William reportedly called her on an encrypted phone line to tell her about her great grandson. She had returned from Windsor Castle to Buckingham Palace earlier on Monday.
According to the Kensington Palace statement "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.
"Her Royal Highness and her child are both doing well and will remain in hospital overnight."
The prince is third in line to the throne, after Princes Charles and William. The recently passed Succession to the Crown Act 2013 ensures a right of accession regardless of gender.
His birth also marks the first time that there have been three heirs in waiting while the monarch is fit and well, said Dickie Arbiter, a former press secretary to the Queen.
The name of the baby is yet to be revealed and sources say it could be a few days before the royal family make the announcement.
The Duchess of Cambridge went into labour just before 6am on Monday. Clarence House said: "The Duchess travelled by car from Kensington Palace to the Lindo Wing at St Mary's Hospital with the Duke of Cambridge."
A spokesman said that her labour had been "progressing as normal". Sky News reported that a number of "bits and bobs" had been bought to Kate by palace staff through the side entrances around lunchtime on Monday.
It is believed Kate had planned to have a natural birth and was going to use hypnotherapy techniques, known as a hypno-birth. Whether she went through with that plan is unknown.
The duchess had been staying at her parent's home in Bucklebury but returned to Kensington Palace. It is thought she will return there after the baby is born - William and Kate's 57-room apartment in the palace was being refurbished and they will not be able to move in until the autumn.
William will also be returning to work as an RAF search and rescue pilot at the end of his two-week paternity leave.
Arbiter said: "Diana was in for 22 hours; she had the baby one day and left the next. Kate might do the same thing."