Count Gaddo della Gherardesca told La Nazione, a newspaper based in Florence, Italy, that the Duchess was "an extraordinary woman", but marriage was a long way off.

The wealthy aristocrat remained guarded about the depth his feelings for the Duchess but said: "In a friendship there is everything, even love."

Party girls: Princesses Eugenie and Beatrice

The father-of-two, who has been separated from his wife Michela for seven years, added: "She has never spoken about an engagement, let alone marriage."

They met through mutual acquaintances and now spend time together, skiing, socialising in London or travelling the world.

The Duchess, 38, has often flown to Tuscany to spend time relaxing in the privacy of the count's home.

It is believed her daughters, princesses Beatrice, 10, and eight-year-old Eugenie, have been invited to the birthday party of the count's 12-year-old daughter Constanza next weekend.

'Sarah is a workhorse'

The count, 49, said he had not seen the duchess since she travelled to Argentina last month for the funeral of her mother Susan Barrantes who was killed in a car crash.

He said: "She was in Argentina and then threw herself into her work.

"Sarah is a workhorse. For this reason I admire her."

The duchess started a new career as a talk show host on satellite TV this week.

The first episode of the weekly hour-long chat show, Sarah ... Surviving Life, was broadcast on Sky One as part of a 10-week run.

'Hell' of press scrutiny

A relationship under international scrutiny is extremely stressful, the count admitted.

He said: "It's hell. Always under the eyes of photographers. Always under the claws of the gossip hunters. It upsets everything."

The count boasts an aristocratic background of 35 generations of landed gentry. His title was created under the Holy Roman Empire in 1344.

The family's wealth is based on wine growing, but he also runs a successful advertising agency in Milan.