A delighted Princess Eugenie revealed she has welcomed her second child, and his birth has shaken up the line of succession.
The little boy, who has been named Ernest George Ronnie Brooksbank, is 13th in line to the throne behind his mum and his older brother, two-year-old August.
This means that everybody in the line from the Duke of Edinburgh - who is in 14th place - shifts down a position.
However, despite having a place in the line of succession and his mum being a princess, baby Ernest will not receive a royal title - and it's down to one royal rule.
Only children of the sovereign, children of the sons of the sovereign and the eldest living son of the Prince of Wales are eligible to be given HRH status and prince and princess titles.
As baby Ernest - and his older brother August - are both great nephews of the current monarch King Charles, they cannot be given titles.
This is different to Prince Harry and Meghan Markle's children Archie and Lilibet, who were recently given prince and princess titles.
When they were born, they were great-grandchildren of the Monarch (the late Elizabeth II), which meant they were eligible for titles.
However, as they are now children of a son of a sovereign, they are allowed to use prince and princess titles.
Announcing the arrival of Ernest yesterday, Eugenie posted two sweet snaps of the newborn - one of him wearing a knitted blue-and-white hat, asleep in a Moses basket, and one of older son August tenderly stroking his brother's head.
She wrote: "Jack and I wanted to share the news that we had our little boy, Ernest George Ronnie Brooksbank on 30th May 2023 at 8.49 weighing 7.1lbs.
"He is named after his great great great Grandfather George, his Grandpa George and my Grandpa Ronald. Augie is loving being a big brother already."
The baby's great-great-great grandfather George is George V, the grandfather of the late Queen, who was King from May 1910 until his death in December 1936 - who had Ernest as one of his middle names.
His first middle name George is in tender tribute to his late grandfather George Brooksbank, Jack's dad, who sadly died in November 2021 at the age of 72 after being unwell for some time following a battle with Covid.
Meanwhile, his second middle name Ronnie is in tribute to Ronald Ferguson, the late father of Eugenie's mum Sarah Ferguson. The former royal polo manager died in 2003 and was dubbed "the galloping major".
