The Duke of Cambridge has said he's "absolutely thrilled" about the birth of Baby Sussex.
His younger brother Harry, 34, and his wife Meghan, 37, welcomed their first child, a baby boy, on Monday.
William and his wife Kate spoke about the latest addition to the royal family as they attended the launch of The King's Cup regatta at the Cutty Sark on Tuesday afternoon.
When asked about the arrival of Baby Sussex, William told reporters: "Obviously thrilled, absolutely thrilled, and obviously looking forward to seeing them."
And William couldn't resist making a joke at his brother's expense, adding: "I'm very pleased and glad to welcome my own brother into the sleep deprivation society that is parenting."
On whether he had any advice for his younger brother, dad-of-three William laughed and said: "Plenty of advice, plenty of advice, but no I wish him all the best and I hope the next few days they can settle down and enjoy having a newborn in their family and the joys that come with that."
VIDEO: William & Kate say they look forward to meeting #babysussex. Wills: “We’re absolutely thrilled & look forward to seeing them in the next few days... I’m v pleased to welcome my brother to the sleep deprivation society that is parenting!” pic.twitter.com/W6ldWWsUgn
— Emily Andrews (@byEmilyAndrews) 7 May 2019
Meanwhile, the Duchess of Cambridge said: "It's such a special time, obviously with [Prince] Louis and [Princess] Charlotte just having had their birthdays it's such a great time of year to have a baby, spring is in the air.
I'm glad to welcome my own brother into the sleep deprivation society that is parenting.
"As William said, we're looking forward to meeting him and finding out what his name's going to be, so it's really exciting for both of them and we wish them all the best.
"These next few weeks are always a bit daunting the first time round so we wish them all the best."
Hours after Meghan and Harry welcomed their son, Kate and William shared a touching message to the couple on the Kensington Palace's Instagram.
Reposting Meghan and Harry's baby announcement, Kate and William's message read: "The Duke and Duchess of Cambridge are delighted with the news of the birth of The Duke and Duchess of Sussex's son today, and look forward to meeting the latest addition to the family."
View this post on Instagram
The Duke and Duchess of Cambridge are delighted with the news of the birth of The Duke and Duchess of Sussex's son today, and look forward to meeting the latest addition to the family. #Repost @sussexroyal ・・・ We are pleased to announce that Their Royal Highnesses The Duke and Duchess of Sussex welcomed their firstborn child in the early morning on May 6th, 2019. Their Royal Highnesses’ son weighs 7lbs. 3oz. The Duchess and baby are both healthy and well, and the couple thank members of the public for their shared excitement and support during this very special time in their lives. More details will be shared in the forthcoming days.
On Monday afternoon, Harry spoke to the media and said the birth of his son was the "most amazing experience".
He added that he was "incredibly proud" of his wife.
The duke said he and Meghan will announce their son's name in the coming days.
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