Princess Eugenie is expecting her third child with husband Jack Brooksbank.
The daughter of Andrew Mountbatten-Windsor and Sarah Ferguson announced the news on Instagram, posting "Baby Brooksbank due 2026!" on Monday.
Princess Eugenie, 36, also shared a photo on the social media platform showing her two sons - August and Ernest - holding an ultrasound image.
A Buckingham Palace statement said the King is "delighted" and that the couple's two children are "very excited" to welcome a new sibling.
Buckingham Palace said: "Her Royal Highness Princess Eugenie and Mr Jack Brooksbank are very pleased to announce that they are expecting their third child together, due this summer.
"August (aged five) and Ernest (aged two) are also very excited to have another sibling join the family.
"His Majesty The King has been informed and is delighted with the news."
The new arrival will be the fifth grandchild of the former Duke and Duchess of York, after the birth of Princess Beatrice's daughter Athena Mapelli Mozzi in January last year.
The news of the baby's arrival came after Andrew was arrested in February on suspicion of misconduct in public office over allegations he shared sensitive information with paedophile financier Jeffrey Epstein. He denies any wrongdoing.
The King also stripped Andrew of his prince title, HRH style and his dukedom because of his friendship with Epstein in November.
The announcement from Buckingham Palace will be seen as a show of support for Eugenie despite the scandal surrounding her father.
Eugenie and her sister Beatrice avoided the traditional royal gathering on Easter Sunday, with the permission of the King, amid the furore over their father.
Read more:
Princess Charlotte portrait released to mark 11th birthday
In pictures: King welcomed by hundreds on Bermuda visit
The princesses, who are granddaughters of the late Queen Elizabeth II, have faced increased public scrutiny after their names appeared in the Epstein files, a cache of millions of documents related to the financier released by the US Department of Justice.
One email exchange suggested their mother took them to see Epstein in the US days after he was released from prison for child sex crimes. The princesses were 19 and 20 at the time.
The baby, who will not be an HRH, will be born 15th in line to the throne, displacing his or her great uncle the Duke of Edinburgh to 16th place.
He or she will also be the 15th great-grandchild of the late Queen Elizabeth II, and the third to be born since her death in 2022.
Eugenie married Mr Brooksbank at Windsor Castle in 2018.
(c) Sky News 2026: King 'delighted' as Princess Eugenie announces she is expecting her third child
Woman and man die in Bristol explosion after 'domestic-related incident'
'Beautiful streaks': Eta Aquariids meteor shower to light up skies over Britain
Food price inflation still rising, as lower income households feel the squeeze, study says
Fish, eels and birds killed in suspected River Spey tributary pollution incident
Scottish soldiers prepare for NATO deployment to Estonia with urban combat drills
UK on verge of joining EU's £78bn loan for Ukraine as Starmer seeks reset with Brussels
Tens of thousands of cancer patients to benefit from one-minute NHS jab
Sir Alex Ferguson taken to hospital after feeling unwell before Manchester United vs Liverpool game
Snooker spectator ejected in disrupted start to world championship final
