Paul Burrell said Diana had revealed to him that she had been more in love with Dr. Khan than "any other man," adding that he had asked her if it would be possible for him to arrange a "private marriage" for the couple.
The "extremely serious" relationship, Burrell claimed, had had lasted for two years, with Dr. Khan a regular visitor to Kensington Palace until the couple split up in July 1997.
It was not immediately clear if Dr. Khan was aware of Diana's intentions to marry him.
Burrell played down reports that Diana had been intending to marry Dodi Al Fayed, the son of Harrods owner Mohamed Al Fayed, and the man who perished with her in a car accident in Paris in 1997.
At the inquest, Burrell is highly likely to be questioned over a reported note from the princess in which she allegedly wrote to him that her husband, Prince Charles, was "planning an accident in my car".
He has also claimed that the Queen once warned him that, "There are powers at work in this country about which we have no knowledge."
Burrell worked for the Royal Family for more than 20 years.
