After refusing for months to co-operate, despite being placed in detention, Christine Deviers-Joncour has written to two investigative judges and accused Mr Dumas of taking inducements from the Elf oil company in the early 1990s.
Contradicting her previous testimony, she said it was Mr Dumas who got her a job with the company, and that while he was foreign minister he accepted presents, bought with Elf's cash, including the shoes and 12 ancient Greek statuettes worth pounds 30,000. The judges are investigating whether Mr Dumas was paid by Elf to drop his opposition to the sale of frigates to Taiwan, a deal brokered by the company.
The allegations make the position of Mr Dumas - head of the constitutional council, which among other things judges the alleged wrongdoings of politicians - virtually untenable.
The latest twist in the case is also uncomfortable for President Jacques Chirac, even though Mr Dumas, as a Socialist, is a political opponent. Mr Chirac is the only person who can bring pressure on Mr Dumas to quit his present post. He has adamantly refused to do so.
Last year the constitutional council, under the chairmanship of Mr Dumas, tagged an unsolicited ruling on to the end of another judgment. In effect, it forbade the French judiciary from investigating the alleged criminal activity of a sitting president. Investigations of the illegal financing of Mr Chirac's party, the neo-Gaullist RPR, have been creeping up the ranks towards the President in recent months.
The Dumas affair is a small corner of a much larger investigation of alleged influence- trafficking and embezzlement at Elf.
Ms Deviers-Joncour, well-known to be the mistress of Mr Dumas, was given an ill-defined job by the company in 1990. She received a high salary, a luxurious apartment and a limitless credit card.
Despite being placed in preventive detention, she refused to co-operate with the judicial investigation of Elf's affairs. She told the judges that Mr Dumas had not rigged her job and had not accepted a centime of Elf's cash.
Her decision to reverse this testimony - both in a letter to the investigating judges and in an interview with Paris Match - comes after a series of slighting and dismissive remarks made by Mr Dumas. Ms Deviers-Joncour infuriated the former foreign minister by describing her long relationship with him in a book entitled The Whore of the Republic.Reuse content