François Fillon and wife Penelope during a campaign rally in Paris | Eric Feferberg/AFP via Getty Images | Eric Feferberg/AFP via Getty Images François Fillon and wife interrogated by police Investigation taking place into payments from presidential candidate to his wife.

PARIS — François Fillon and his wife Penelope were interrogated Monday afternoon by police investigating alleged misuse of public funds by the conservative candidate to be president.

The news, first broadcast by French TV channel BFM TV, was confirmed to POLITICO by a senior Fillon aide.

French satirical weekly Le Canard Enchainé said last week that Penelope Fillon was paid €500,000 over eight years when employed as a parliamentary aide to her husband and his successor at the National Assembly.

How much work she did has been questioned and Fillon pledged that he would “defend [his] and his wife’s honor” and produce proof that he would show to the police.

The French financial public prosecutor decided to launch a preliminary inquiry into the matter, which may result in a formal investigation.

Fillon said he wanted to be interrogated “as quickly as possible,” notably because he has pledged to withdraw from the presidential race if placed under formal investigation.

The police on Monday also interrogated Marc Ladreit de Lacharrière, a businessman friend of Fillon's and owner of a literary review that paid the candidate’s wife €100,000 for “consulting work.”

Officials of conservative party Les Républicains are worried that they won't be able to find a credible alternative if the prosecutor’s decision to comes too late in the race.

The first round of the French presidential election is due April 23 with a run-off on May 3.