Princess Charlene of Monaco has been taken to a treatment facility outside Monaco.
This comes just days after the royal returned to the principality after spending eight months in South Africa.
The decision to seek medical care was made jointly by Charlene, her husband Prince Albert and her brothers.
In an interview with People, Monaco's sovereign prince said that the 43-year-old princess was suffering from profound “exhaustion, both emotional and physical”.
He said her recovery would require clinical care lasting several weeks at minimum.
Her current state, he said, was the result “of several factors which are private matters. She was clearly exhausted, physically and emotionally. She was overwhelmed and couldn't face official duties, life in general or even family life”.
According to Albert, seeking treatment elsewhere in Europe was a solution that the princess already favoured.
“She had already made her decision, and we only wanted her to confirm it in front of us. She wanted this. She already knew the best thing to do was to go and have a rest and have a real medically framed treatment. And not in Monaco. For privacy reasons, it would have to be some place outside of Monaco,” he told the publication.
Earlier this week it was announced by the palace that the princess would not take part in the principality's national day celebrations.
The palace said Charlene, a former Olympian, would convalesce at a secret location and that she would only resume her public duties once her health allowed it.
“A period of calm and rest is necessary to ensure the very best recovery for Princess Charlene's health,” the palace said.
“Having battled with poor health over the past few months, the princess is currently convalescing and will continue to do so for the coming weeks,” it added.
In his interview with People, Albert dismissed rumours that there was a problem with his marriage.
“I'm probably going to say this several times, but this has nothing to do with our relationship. I want to make that very clear. These are not problems within our relationship; not with the relationship between a husband and wife. It's of a different nature.”