Andrew - whose 10-year-marriage to Sarah ended in divorce in 1996 - invited the duchess to move into his Royal Lodge, on royal estate Windsor Great Park, after she accidentally set fire to her Surrey home, Dolphin House, last week.
Britain's Prince Andrew and his ex-wife Sarah Ferguson, the Duchess of York, are living together again.
Andrew - whose 10-year-marriage to Sarah ended in divorce in 1996 - invited the duchess to move into his Royal Lodge, on royal estate Windsor Great Park, after she accidentally set fire to her Surrey home, Dolphin House, last week.
A source told Britain's The Sun newspaper: "It's been a long time since they shared a home together but it seems the events of last week have caused the unthinkable to happen.
"The fire in her bathroom has left her home stinking of smoke and it may take six weeks to put things right."
Sarah - who reportedly started the fire by leaving a scented candle alight in her toilet - is expected to stay with Andrew for the next two weeks before the pair take their daughters Princesses Beatrice, 19 and Eugenie, 17, to Switzerland for a skiing holiday.
Andrew's father Prince Philip is said to be furious the pair are living together again.
The source added: "Philip hasn't spoken to Sarah since she split from Andrew in 1992 and he'll be furious. This is the news he has been dreading."
Meanwhile, Andrew has sold his former marital home Sunninghill Park, near Ascot, for £15 million.
The sprawling mansion was built as a gift from Queen Elizabeth to Andrew and Sarah when they got married in 1986.
After Sarah and Andrew officially separated in 1992, the duchess continued living on and off at the property until 2004, when Andrew moved to Royal Lodge.
The queen retained ownership of the Sunninghill Park until 2000 when she signed it over to Andrew, who put it on the market four years ago.
The house is believed to have been bought by a businessman from Kazakhstan.
News of the sale comes just as Andrew has become embroiled in a row over expenses.
The prince, nicknamed Air Miles Andy because of his frequent travelling, has sparked criticism by reportedly planning an official tour of the US in a private jet at a cost to taxpayers of £100,000.
Prince Andrew
Sarah Ferguson
Duchess of York
