When asked about his son as he arrived for the service, William said the family were "in good form, luckily".
The names of his siblings, Prince George and Princess Charlotte, were announced two days after they born.
But does the Duchess of Cambridge's post-birth aesthetic send the wrong message to expectant mothers across the nation? "Let's go now", she said, to which William replied, "Sure", before they walked back inside.
- The new baby will be a prince or princess of Cambridge and enjoy the prefix title of his or her royal highness (HRH).
While another tweeted, 'Kate Middleton had the baby 7 hours prior to this photo.
William and Kate revealed George's name - George Alexander Louis - two days after his July 22, 2013, birth.
Did Will get all mushy and tell his wife that he loved her and that she was doing great even though she just gave birth and had to pose for the media?
Eugenie is due to Wednesday Jack Brooksbank after seven years together on October 12 in St George's Chapel at Windsor Castle - the same location where Prince Harry and Meghan Markle will tie the knot on May 19.
Prince George, 4, and Princess Charlotte, 2, were snapped visiting their baby brother after school on Monday afternoon, with Charlotte sparking an online meltdown as she perfected the royal wave for photographers.
Why haven't they announced his name? .