Princess Stephanie of Monaco and her three young children had to be evacuated from their Alpine ski-station apartment in the early hours of Sunday after fire broke out in the cellar, police said.
The blaze, which quickly sent noxious, thick, white fumes billowing from burning plastic chairs, was believed to have been sparked by a short circuit in an electric radiator.
The princess and her three children, Louis, Pauline and Camille, were all unhurt and were taken to a nearby hotel at the Auron ski station in Alpes-Maritimes for the rest of the night.
They returned home to the Mediterranean principality of Monaco Sunday afternoon.
Stephanie is the third child of Prince Rainier of Monaco and Princess Grace, who died in a car crash in 1982.