Factbox: A prince is born - Third child for Prince William and wife Kate

LONDON (Reuters) - Kate, the wife of Britain's Prince William, gave birth to a boy at a hospital in London on Monday, the third child for the royal couple.

WHAT DID KENSINGTON PALACE SAY?

"Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs.

"The baby weighs 8lbs 7oz [3.8 kg].

"The Duke of Cambridge was present for the birth.

"Her Royal Highness and her child are both doing well.

"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.

"Their Royal Highnesses would like to thank all staff at the hospital for the care and treatment they have received. They would also like to thank everyone for their warm wishes."

WHAT CEREMONY IS INVOLVED?

As is tradition, the framed notice of birth will go on display on a ceremonial easel on the forecourt of Buckingham Palace.

"The framed bulletin will be brought out of the Privy Purse Door and carried across the forecourt, to be placed on the easel," Buckingham Palace said.

The practice of posting a bulletin on the occasion of a royal birth has gone on for at least as long as Buckingham Palace has been the Sovereign’s official residence (from 1837).

The bulletin will be on display for approximately 24 hours. After it comes down, it is sent to the Privy Council Office in order that the details of the official notice may be recorded in the Privy Council records.

HOW IMPORTANT IS THE NEW PRINCE?

The new prince is Queen Elizabeth's sixth great-grandchild and fifth-in-line to the British throne behind siblings George, 4, his two-year-old sister Charlotte, their father William, and grandfather Prince Charles, who is heir.

A 2013 change to the law means the boy will not supplant his older sister Charlotte in the line of succession. Before that change younger males would take precedence over older female siblings.

(For a graphic on the line of succession, please click http://fingfx.thomsonreuters.com/gfx/rngs/BRITAIN-ROYALS-BABY/010062CS3Z2/BRITAIN-ROYALS-BABY.jpg)

WHAT IS THE NAME?

It is not yet clear. An announcement will come soon.

HOSPITAL MOVEMENTS

Kate left hospital, flanked by William and holding the baby in her arms, on Monday evening. She and William smiled and waved at hundreds of assembled well-wishers and journalists before heading back to Kensington Palace.

Earlier, William had brought George and Charlotte to meet their new brother as well-wishers cheered outside the hospital.

Princess Charlotte, 2, turned and waved. George, 4, did not wave.

CONGRATULATIONS:

- BRITISH PM THERESA MAY:

"My warmest congratulations to the Duke and Duchess of Cambridge on the birth of their baby boy. I wish them great happiness for the future."

- THE ARCHBISHOP OF CANTERBURY, SPIRITUAL HEAD OF THE ANGLICAN COMMUNION:

"Congratulations to The Duke and Duchess of Cambridge on the safe delivery of their baby, a brother for Prince George and Princess Charlotte. May God bless them and all of their children with love, happiness and health."

- BRITISH FOREIGN SECRETARY BORIS JOHNSON:

"Huge congratulations to Their Royal Highnesses The Duke and Duchess of Cambridge on the safe delivery of their baby boy today."

- BRITISH CHANCELLOR OF THE EXCHEQUER PHILIP HAMMOND:

"Congratulations to the Duke and Duchess of Cambridge on the arrival of their baby boy."

- THE ROYAL NAVY:

The Royal Navy sent out a picture showing crew members of the HMS Albion standing on deck at sea in a "BOY!" formation.

- UK GOVERNMENT

Flags on UK Government Buildings will fly at full mast on Tuesday, April 24, in celebration of the birth.

- CANADIAN PRIME MINISTER JUSTIN TRUDEAU: "Canada welcomes a baby boy to the Royal Family! Sophie & I send our congratulations to William and Kate, the Duke and Duchess of Cambridge, and to George and Charlotte on the new arrival."

- BRITISH OPPOSITION LEADER JEREMY CORBYN: "Congratulations to Kate and William on the birth of their baby boy. I wish them all the very best."

(Reporting by Michael Holden and Guy Faulconbridge; Editing by Gareth Jones)