The two doctors have just examined the President, who has been complaining of pains in his thigh. He has also had tests at Val-de-Grace hospital, visiting secretly in Dr Gubler's ageing Citroen and registering as Albert Blot - the name of the hospital director's brother-in-law.
"My duty is not to conceal the truth from you," says the surgeon. "You have cancer of the prostate which has spread into your bones, and this spreading is quite far advanced."
The President replies, under his breath: "I am done for."
"You can never say that you are finished," Prof Steg insists. "With Dr Gubler, I will do what can be done."
"Enough of that," comes the answer. "I am done for."
This grim little scene was laid before the French public last week by Dr Gubler in a book entitled The Big Secret. The book was immediately ordered to be withdrawn from sale, not because it was untrue - the vast majority of its claims have gone unchallenged - but because it was deemed to breach professional confidentiality and intrude into the privacy of a man and his family barely a week after his death.
Yet The Big Secret is also the extraordinary story of a Very Big Lie. During the election campaign of 1981 Mr Mitterrand undertook to publish regular bulletins on his own health. This was a proof of "transparency", in contrast to the days of Georges Pompidou, who died in office of cancer in 1974 after repeatedly denying he had anything worse than a cold.
Mr Mitterrand reacted to his illness, Dr Gubler says, by declaring it "a state secret". For 11 years the bulletins were published, but instead of starting "The President's prostate cancer...." they discussed minor ailments and concluded blithely that he was in good health.
It did not stop there. As Dr Gubler put it: "The reign of the generalised lie began." Mr Mitterrand needed daily medical treatment. Abroad, he got it secretly in the dead of night wherever he was staying. In communist eastern Europe the treatment was given in silence for fear of listening devices.
Every needle and bottle was locked in a special suitcase and taken home in diplomatic baggage for destruction.
The cancer responded to the treatment and Mr Mitterrand came to believe, according to Dr Gubler, that he had been cured.
Thus he did not consult the doctor before standing for the presidency again in 1988 nor, as far as Dr Gubler was aware, seek any other medical advice. A man of 71 with known prostate cancer, living on borrowed time, decided he was fit to lead France for seven more years.
He won his gamble and lived to finish his second term last year, the century's longest serving French president. But, as Liberation newspaper pointed out, the French people were also involved in the bet, only without knowing it.
By 1992 the cancer was advancing again. Two operations, chemotherapy and radiotherapy followed over two years.
By now there was no hiding the illness. Mr Mitterrand acknowledged on television that he had cancer but insisted he would be well enough to finish his term.
This, according to Dr Gubler, was the last lie. He claims, though others have vigorously denied it since, that for his last six months as President, Francois Mitterrand was incapable of discharging the functions of his office.
The book portrays a leader who spent all day in bed. "He arrived at the Elysee at 9.30am and went straight back to bed until lunchtime... He did not work because he was interested in nothing besides his illness."
During this time, Dr Gubler says, the then Prime Minister, Edouard Balladur, was happy to proceed as if nothing was amiss. "The absence of the President served his interests."Reuse content