The Duke and Duchess of Sussex have used Instagram to announce the birth of their first child, a son.

The boy, as yet unnamed, was born at 5:26 am on Monday, weighing 3 kg, with the news being announced to the wider world at around 2:40 pm local time.

The new arrival, who becomes seventh in line to the British throne, will be revealed to the public on Wednesday after the couple said they wanted to spend time as a family to enjoy the birth privately, before sharing it with the world at large.

His arrival means the Queen, who recently celebrated her 93rd birthday, now has eight great-grandchildren.

The official royal family Twitter account said the Queen and wider royal family including Prince Charles and the Duke and Duchess of Cambridge, were "delighted with the news", while adding that the Duchess's mother, Doria Ragland, was "overjoyed" at the birth of her first grandchild, just under 12 months after the couple were married at Windsor Castle.