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, Kensington Palace announced on Twitter. The boy was born at 11:01 am, hours after Kate was transported to London's St. Mary's Hospital in labor.
Kate and her child "are both doing well," according to the statement.
The child, who is the royal couple's third child and second son, is the fifth in line to the throne.
The name of the newborn child was not immediately announced.
The couple's second child, Princess Charlotte, turns three in May. She started attending nursery school in London in January. The oldest of the royal siblings, Prince George, is now four and began school in September 2017.
British PM May has congratulated Prince William and his wife Kate on the birth of the baby boy.
Internet users have followed suit, rushing to Twitter to congratulate the Royal couple.