Marion Maréchal-Le Pen, the niece of defeated far-right French presidential candidate Marine Le Pen, is to quit politics, French media report.
Ms Maréchal-Le Pen, 27, who is an MP for the National Front (FN), had been seen by some as a future leader of the party.
She is the granddaughter of FN founder Jean-Marie Le Pen.
She is one of the best known figures in the party and one of only two FN lawmakers in the outgoing parliament.
Analysts say she takes more of a hardline position than her aunt.
According to Le Figaro, Ms Maréchal-Le Pen will announce on Wednesday her intention not to stand for a new term in parliamentary elections in June. She will also quit her position as president of the FN in the south-eastern region of Provence-Alpes-Côte d’Azur.
It is understood she wishes to spend more time with her young daughter, the newspaper adds.
The party would not confirm the report but senior FN official Bruno Gollnisch told reporters it would not be totally unexpected.
“I think it’s in the works, but I will let her announce it if she wants to,” he said.
Sky News reports that Le Pen’s grandfather, Jean Marie Le Pen, founder of Front National, is critical of his granddaughter’s move.
The younger politician is more conservative on social and economic issues and she took part in rallies against gay marriage laws, while her aunt avoided them.
She said her relative’s decision to soften her stance on seeking to quit the euro had come too late for voters concerned about that part of her programme.
Other differences between the two include their relationship with the party’s founder, Jean-Marie Le Pen.
Ms Le Pen is estranged from her father, while Ms Marechal-Le Pen and him have closer ties.
Speaking to Le Figaro, he called his granddaughter’s move “a desertion”.
He said: “This will create a huge disappointment… Marion represented a hope for the future for many FN voters and activists.”
Political expert Joel Gombin said of her decision: “This raises a lot of questions on how the party will evolve.
“It risks leaving a number of people orphan, and could trigger some fighting among those would like to take over from her at the head of the ultra-conservative faction of the FN.”