She has so far written one successful Mills & Boon novel, titled Her Heart for a Compass, with another on the way, and has signed a 22-book deal as a children's author. She also has other business interests, a source said.
The mews house was purchased from the Grosvenor estate of the Duke of Westminster, one of the richest men in Britain. Prince Andrew played no part in the deal.
The Duke and Duchess still have an outstanding debt relating to the Swiss chalet they own jointly.
They both currently live at Royal Lodge near to Windsor Castle, albeit separately. It is rumoured that the Duke and his ex-wife could be asked to leave the large property when the Queen dies, after he "stepped back" from official duties.
The Duke signed a 75-year lease on the property in 2003, but it is understood that an agreement could be broken as long as he is appropriately compensated.
The Prince of Wales, understood to be a key driving force behind his brother's disappearance from public life, is reportedly minded to ask him to move out of the large Windsor property once he is king. Sources say it is within the gift of the monarch to terminate the Royal Lodge arrangement.
The Duke of York no longer has an apartment in Buckingham Palace after the wing it was situated in was emptied as part of a wider refurbishment.
The Duchess's son-in-law, Princess Beatrice's husband Eduardo Mapelli Mozzi works in luxury property.
