In other words, his uncle, Prince Harry, now gets bumped down to fourth place.
As for who rounds out the top 10, well, that would be Princess Beatrice, Princess Eugenie, Prince Edward, Viscount Severn and the Lady Louise Windsor.
Mind you, had the bundle of joy been a girl, she too, would have been third in line, thanks to a change made earlier this year.
The Succession to the Crown Bill, determining that the Duke and Duchess of Cambridge's first child will be a monarch, regardless of its sex, was approved by Queen Elizabeth II back in January.
Of course, with the arrival of the little fella, the change is rather a moot point. (At least for now.)
On Monday, it was formally announced that the Duke and Duchess of Cambridge had welcomed their first child together.
Kensington Palace announced that the couple's firstborn weighed in at 8 lbs 6 oz. and arrived at 4:24 p.m. London time.
"Her Royal Highness and her child are both doing well and will remain in the hospital overnight," a statement read.
A Buckingham Palace spokesman said: "The Queen and Duke of Edinburgh are delighted at the news."