Prince William's dad joke to congratulate brother Harry on Baby Sussex

Prince William made a joke to welcome his younger brother to the world of parenting. Photo / Getty Images

Prince William has welcomed his brother Prince Harry to the "sleep deprivation society" following the birth of his younger sibling's first child.

The 36-year-old second-in-line to the British throne - who has Prince George, 5, Princess Charlotte, 4, and 13-month-old Prince Louis with his wife, Duchess Catherine - stepped out to announce the launch of The King's Cup regatta at the Cutty Sark in London on Tuesday afternoon, and made sure to congratulate the Duke and Duchess of Sussex on their new arrival.

William admitted he is "thrilled" for the couple and will meet his nephew in the "next few days".

Speaking at the event, William said: "[We are] absolutely thrilled and looking forward to seeing him in the next few days when he's quietened down. I'm very pleased and glad to welcome my brother to the sleep deprivation society that is parenting! So we'll be looking forward to that."

William's words of congratulations come after his and Harry's father Prince Charles revealed that he is "delighted" to welcome his fourth grandchild into the world and can't wait to meet the baby when he returns from his visit to Berlin, Germany, with his wife Camilla.

Prince William is thrilled his brother will now experience the highs and lows of parenting. Photo / Getty Images

During his visit, The Prince of Wales said: "We couldn't be more delighted at the news and we're looking forward to meeting the baby when we return."

Meghan Markle, Duchess of Sussex and her 34-year-old husband Prince Harry welcomed their son, who weighed 7lb 6oz, into the world on Monday. They are yet to choose a name for the tot, the newest member of the British royal family.