Gun Salute throughout London is to mark the arrival of the Duke and Duchess of Cambridge's third child.
The couple's second son, fifth in line of succession, was arrested on Monday in the Lindo Wing of St Mary's Hospital, London, weighing 8lb 7oz
The traditional salute will be at 14:00 BST fired from the Tower of London and Hyde Park.
The name of the new prince has not yet been announced, but the family has returned Home of the Kensington Palace
Gun Salutes are used to mark every birth of a prince or a princess.
The palace said that a name would be revealed in due course, but provisionally a formal notice of the birth of the child (19659007) Arthur, James, Philip and Albert are among the bookmakers' favorites.
The prince's siblings, Prince George and Princess Charlotte, visited their younger brother at the hospital on Monday.
Catherine was inducted into the Lindo Wing at 6:00 am BST on Monday, birth was announced shortly after 1:00 pm
Masses gathered in front of the Paddington Hospital, with some well-wishers who had been in the hospital for more than two weeks camped.  When Prince William left with his new son, he said that the couple was very happy and joking now had "three times the worry".
In 2013, the law that enabled Princess Charlotte to change her fourth place
Before, younger royal men would have outstripped their older sisters.
Will the new prince be king?
To become king or queen, like the third born king child is rare – and has still happened in Windsor's current home.
But the third child of George III and Queen Charlotte, William IV, took over the task and ruled from 1830 to 1837.
The Hanoverian king entered the throne at age 64, when his older brother, George IV, died an heir died.
He became the next in line when he was 62 and his other elder brother, Frederick, Duke of York, died.