According to NBC News:
The Duchess of Cambridge gave birth to a baby son Monday, Kensington Palace announced.
It is her third child with Britain’s Prince William, who accompanied his wife to the hospital. His name was not immediately announced.
The duchess had her two other children, Prince George in 2013 and Princess Charlotte in 2015, at the same hospital. Princes William and Harry were also born there.
As she did during her first two pregnancies, Kate suffered from severe morning sickness, known as hyperemesis gravidarum. It was so severe during her first pregnancy in 2012 that she had to be hospitalized.
