Kensington Palace said the baby was born at 1001 GMT and weighs 8 lbs 7oz (3.9 kg). William was present for the birth at St Mary’s Hospital in west London where their other two children, George and Charlotte, were also born, it added.
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 and heir Prince Charles.
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.