It is the classic tale of an aristocratic inheritance feud, albeit with a distinctly modern twist.

The blue blood in the long, illustrious line of the Doria Pamphilj family ran out a generation ago, leaving the Italian courts to decide who is the rightful heir to the Renaissance palaces, the magnificent art collection, and the £1 billion fortune. Should it be the four daughters of the staunchly Catholic sister? Or the two children conceived by her gay brother with the help of a surrogate mother?

At the centre of the saga are Princess Gesine and Prince Jonathan, two British-born orphans who were plucked from a London orphanage in the 1960s and adopted by a descendant of one of Italy’s most noble families.

They were known only as Archibald and Mary before winning the heart of Princess Orietta Pogson Doria Pamphilj, who whisked them out of postwar England and introduced them to a new world of gilded palaces, private nannies and priceless works of art. Not biologically related, they were renamed Jonathan Paul and Gesine, took the titles Prince and Princess, and were raised as brother and sister.

The pair are now locked in a legal battle as to whose children should inherit the estate. An Italian court is due to give its verdict this month.

Prince Jonathan and Princess Gesine inherited 14 noble titles, two palaces, including a 1,000-room palazzo in central Rome, and one of the world’s greatest private art collections after the death of their adopted mother in December 2000.

Princess Gesine, who has four daughters with her husband Massimiliano Floridi, has refused to recognise her brother’s children as legitimate heirs.

Prince Jonathan, 46, and his Brazilian civil partner Elson Edeno Braga, used two surrogates to have Filippo Andrea, 2, who was born in the Ukraine, and Emily, 3, born in the United States.

Princess Gesine, a staunch Catholic who reportedly disapproves of his lifestyle, says that she is asking the courts to rule on the paternity of the two children to prevent what she regards as a potential raid on the family fortune in years to come.

“What the court has to decide is the paternity of these two children. Under Italian law they have no official standing — just because you say they are your children it doesn’t mean they are,” she said.

“I don’t agree at all with surrogate mothers — people have a right to children but children have a right to parents. It has caused a lot of tension with my brother and our relationship has suffered.

“The woman who gives birth doesn’t renounce her right to motherhood and what’s to say that in ten years time she won’t come along with all the paperwork to say she is the mother and make a claim on the estate?

“At first I tried to work something out together with my brother but it didn’t work out so I took it to the courts, and now they will have to decide,” On her death at the age of 78, Princess Orietta passed down a portfolio of lavish properties including the Palazzo Pamphilj in Rome, the Palazzo del Principe in Genoa and a country estate.

Her art collection includes more than 650 works by artists including Raphael, Titian, Caravaggio and the iconic portrait by Velasquez of Pope Innocent X.

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