French Justice Minister Eric Dupond-Moretti faced fresh difficulties on Wednesday after admitting to a "mistake" on his tax form that saw him fail to declare €300,000 in royalties. 

The 60-year-old was the star turn in a cabinet reshuffle announced almost exactly a year ago when he decided to swap his life as one of the country's most successful and famous lawyers for a new career in politics.

As well as seeing his considerable wealth frequently targeted by opponents, he faces legal problems which are expected to see him charged next week for abusing his position as a minister to settle scores with opponents from his legal career.

On Wednesday, following media reports about his tax affairs, an aide admitted to AFP that he had failed to declare €300,000 in royalties paid to him during the 2018-2019 tax year stemming from a theatre production.

"The tax has been paid and the tax status of the minister is completely regularised, and his good faith has been demonstrated," an aide said on condition of anonymity. 

The source referred to an "error" by the minister's previous accountant identified during a tax audit overseen by the HATVP watchdog, which is responsible for vetting the financial affairs of ministers.

The expected charges against him for abuse of power, which he denies, relate to an administrative investigation he ordered after becoming minister against three magistrates.

Dupond-Moretti, famed for his record of acquitting defendants, swore as recently as 2018 that he would never be justice minister, saying no one would have the "utterly absurd" idea.

Last month, he suffered a major electoral defeat after appearing on the ballot for the first time in regional elections.

The undeclared royalties relate to his own one-man theatre show called "Eric Dupond-Moretti to the Bar" which he appeared in while running his law firm.

Aides have ruled out him resigning and President Emmanuel Macron is thought to be keen to retain a senior minister who appears regularly in the media and has announced ambitious reforms for the judicial system.