Peter Phillips, the Queen's eldest grandson, is to separate from his wife Autumn, it is reported.
The 42-year-old, who is 15th in line to the throne, is the son of Princess Anne and her first husband Captain Mark Phillips.
He is said to be in "total shock" and "devastated" by his 41-year-old wife's decision to return to Canada, with their daughters Savannah, nine, and Isla, seven, who have dual citizenship.
The Queen is reportedly "saddened" by the news.
It follows the decision by Prince Harry and Meghan Markle to step down as senior royals and relocate to Canada.
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A friend is reported as saying: "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."
Peter Phillips met his wife during the 2003 Formula One Grand Prix in her home city of Montreal, where they had both been working.
She did not realise his status until she spotted him on TV after their first meeting.
They married at St George's Chapel in Windsor.
Buckingham Palace has not commented on the reports.
