Peter Phillips has reportedly split from his wife.
The 42-year-old marketing consultant - who is the son of Princess Anne and her ex-husband Captain Mark Phillips - was said to have been stunned when spouse Autumn told him she wanted to end their 12-year marriage.
A source told The Sun newspaper: "Peter is absolutely devastated by this and just didn't see it coming.
"He thought he was happily married and had the perfect family with two lovely daughters. But he is now in total shock.
"Autumn is a wonderful wife and mother and a very intelligent woman but she's been telling her friends for some time that there were issues.
It is believed the couple - who have daughters Savannah, nine, and Isla, seven, together - simply "grew apart".
An insider said: "Certainly none of us think either Peter or Autumn are involved with anyone else.
"It just seems they have grown apart but it's come as a bolt out of the blue for Peter and he's very upset."
Peter's grandmother, Queen Elizabeth, is said to be very close to the couple so would likely be very upset by the news.
The source said: "She is a favourite of the Queen and I'm sure Her Majesty will be very upset by this as well."
Another insider added: "Peter Phillips has always been a favourite of hers and Prince Philip and she will be crestfallen by this, especially on top of all the other bad news."
Peter and Autumn met in 2003 when they were both working at the Formula One Grand Prix in her home city of Montreal.
The management consultant had no idea Peter was the queen's grandson until she saw a picture of him on TV several weeks later.
He proposed in 2007 after seeking permission from his future father-in-law and, after Autumn converted from Catholicism to Church of England so Peter could stay in the line of succession, they tied the knot in St. George's Chapel at Windsor Castle in May 2008.