Former French President Nicolas Sarkozy has been ‘scandalously’ charged with taking financial advantage of France’s richest woman, elderly L'Oreal heiress Liliane Bettencourt, in a scandal over illegal campaign funding.

Sarkozy was placed under formal investigation on Thursday, his lawyer told AFP, adding that he would immediately appeal the “unfair and incoherent” decision.

This comes after the former president was unexpectedly summoned for a face-to-face encounter with Bettencourt staff members over claims he accepted funds from the heiress to illegally finance his 2007 election campaign. Sarkozy has repeatedly denied the allegations.

A statement given by the prosecutor in the city of Bordeaux after the hearing explained that "Nicolas Sarkozy, who benefits from the presumption of innocence, had been notified that he has been placed under formal investigation for taking advantage of a vulnerable person in February 2007 and during 2007 to the detriment of Liliane Bettencourt."

The claims do not come as a complete surprise, as the former president was already questioned by judges in November, but they chose not to pursue a full investigation. The suspicions date back to three years ago when a woman working for Bettencourt as an accountant allegedly spotted plans for a large cash withdrawal to be made with the intention of supporting Sarkozy’s presidential campaign.

Liliane Bettencourt, 90, is France’s richest and the world’s third-richest woman. Her mental frailty supposedly played a part in how the investigation is being framed.

Sarkozy’s lawyer Thierry Herzog said his client, “considers the treatment inflicted upon him as scandalous” and that they will be appealing.

Sarkozy maintains that he visited her home only once during the election campaign to meet Bettencourt’s late husband. However Calire Thaibout, Bettencourt’s former accountant, told police in 2010 that she had passed envelopes stuffed with cash to Patrice de Maistre, which were then to be given to Sarkozy’s campaign treasurer Eric Woerth.

Investigators believe that up to four million euro (US$5.2 million) of Bettencourt’s cash reached the coffers of Sarkozy’s UMP party.

Although Sarkozy has left major politics, he remains a potential conservative candidate for the next presidential race in 2017.

His supporters say that the allegations are aimed at besmirching his image and preventing his political comeback.