William and Kate welcomed their third child on Monday - which is also St. George's day, England's national day.
"Her Royal Highness along with also her child are both successful", the conversation continued.
The baby's sex was a surprise to William and Kate, who chose not to find out what they were having.
Before going on leave the Duchess of Cambridge carried out her last official engagement.
One of London's tallest buildings, the BT Tower, projected a celebratory message for the birth of the prince.
As of this writing, Kensington Palace has not officially released the new royal baby's name nor any pictures of him.
The new child will be fifth in line to the British throne, behind big sister Charlotte and pushing uncle Prince Harry one place down the line of succession to sixth.
William and Kate Wednesday in 2011 and also have just two other kids: Prince George, 4, along with Princess Charlotte, that turns 3. The Duke of Cambridge was present for the birth.
Fans were immediately excited about the prospect of another royal baby, and they're even more thrilled now that the little bundle of joy is here.
Royal fanatics have been camped outside the hospital wing for several days in anticipation.
Kensington Palace announced Kate's pregnancy in September.
She said: "I wish them great happiness for the future".
The official announcement of the birth was made by placing a notice on an easel in the forecourt of the queen's London home, Buckingham Palace, a tradition that has been in place since it became the sovereign's official residence in 1837. The young royal's name is not expected to be announced until tomorrow.
Until recently, the rules of succession favoured male heirs, so a younger brother would jump ahead of an elder sister in the line for the throne. This time around, it kept her from taking Prince George to his first day of school.
The birth comes just weeks before the wedding of Harry and Markle at St. George's Chapel in Windsor on May 19.