Kasia Gallanio, 45, was denied custody of her three daughters and was living in Spain while battling problems with alcoholism and depression, the French newspaper Le Parisien reported.
Her lifeless body was discovered inside the property by police on Sunday.
Gallanio, who was born in Los Angeles and of Polish origin, married Abdelaziz bin Khalifa al-Thani, 73, the uncle of the Emir of Qatar, in 2004 and the couple went on to have three daughters together.
However, they fought a bitter custody battle for over a decade following allegations that he sexually assaulted his eldest child. He has always denied the allegations.
She had been living in one of the couple’s homes in Marbella , while the three children remained with their father living in Paris.
A post-mortem is still due to take place.
Her former husband is a former government minister in Qatar but has lived in France for many years. He was apparently forced into exile following an alleged failed coup against the leader of Qatar in the 1990s.
He lives with their three daughters on the luxurious Avenue Montaigne off the Champs-Elysees.
Louis Spagnuolo, a close friend of the former princess in Marbella, told the Spanish expat newspaper Olive Press that Gallanio was “against drugs” and not an alcoholic.
“I knew her very, very well and am devastated by the news,” he said. “She was a very good person and those who knew her loved her.
“She loved her daughters beyond belief and would never leave them. She was dead against drugs and was never an alcoholic.”