Following the birth of Meghan Markle and Prince Harry's first child on Monday, a baby boy, Harry's older brother and his wife—who are parents themselves to Prince George, 5, Princess Charlotte, 4, and Prince Louis, 1—added their congratulations.
"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," Kensington Palace said in a statement.
Following the announcement that Meghan was expecting, the palace released a statement from William and Kate saying they were "delighted" for the newlyweds.
Shortly after Meghan's pregnancy was announced, Kate shared her excitement about the news while chatting with the crowd gathered during a November visit to Leicester University.
When a fan asked the royal mom of three if she was excited about Prince Harry and Meghan's baby on the way, Kate immediately responded: "Absolutely!"
"It's such a special time to have little kiddies," she shared. "And a cousin for George and Charlotte, as well, and Louis. It'll be really special."
Earlier in the day, Queen Elizabeth, great-grandmother to the newborn, also added her welcome to the newest member of the family.
"The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, The Duke and Duchess of Cambridge, Lady Jane Fellowes, Lady Sarah McCorquodale and Earl Spencer have been informed and are delighted with the news," Buckingham Palace said in a statement.
Meghan's mother, Doria Ragland, said she was "overjoyed" about becoming a first-time grandmother.
"The Duchess's mother, Doria Ragland, who is overjoyed by the arrival of her first grandchild, is with Their Royal Highnesses at Frogmore Cottage. Her Royal Highness and the baby are both doing well," the statement read.