And while everyone was busy taking photos and gushing over how cute the royal toddlers looked, it seems we all missed a hilarious cheeky moment between the two.
Fittingly, her brother's birth will not bump Charlotte's place in the line of succession-a history-making move, since the Succession to the Crown act, which favoured male heirs, was changed in 2013.
"That is definitely Prince George FLICKING the back of Princess Charlotte's head as they enter the Lindo Wing", one amused Twitter user wrote.
After Kate had given birth to the new prince, William left the hospital to go home to Kensington Palace and pick up Charlotte and Prince George, who was still in his school uniform for the first meeting.
Cardinals reportedly 'making a lot of noise about moving up' in draft
I promise that Josh Allen will not be any good which is why I am also positive the Browns will draft him, it's just what they do. But perhaps the most intriguing quarterback question could come down to this: Lamar Jackson , Kyle Lauletta or Mason Rudolph?
A confident Princess Charlotte proved she has already mastered the royal wave as she melted hearts by turning to face the cameras before going inside. "Typical older brother", another person said.
The name of the royal baby is yet to be announced.
Others claimed that the Prince was simply trying to also pat his sister's back and thought it was a sweet moment between the siblings.
"Thrice the worry now!" joked Prince William on Monday when he and the Duchess of Cambridge gave the world the first glimpse of their third child outside St Mary's Hospital in London, seven hours after the baby was born. We would like to send our most honest congratulations to the couple following the birth.
With the Duke and Duchess involving their children in both royal and life engagements, the princess has not been one to shy away from the camera.