(CNN) -- An investigative judge has placed former French President Nicolas Sarkozy under formal investigation for breach of trust, accusing him of taking advantage of elderly L'Oreal cosmetic heiress Liliane Bettencourt to help fund his 2007 campaign, Sarkozy's attorney said, according to CNN affiliate BFM-TV.
The former president was summoned to appear at Judge Jean-Michel Gentil's office in Bordeaux on Thursday in a case in which he is suspected of accepting illegal contributions from Bettencourt and her staff, BFM-TV said.
His lawyer, Thierry Herzog, said that he intends to appeal the ruling, according to BFM-TV.
The Bettencourt scandal has fascinated France since questions about the finances of France's richest woman emerged in 2011 amid a family feud.
Although formal, the investigation of Sarkozy, 58, is considered preliminary, and could lead to trial or may go no further.
The son of a Hungarian refugee father and French mother, Sarkozy was 28 when he became mayor of Neuilly, a Paris suburb. He left that post in 2002 to serve as interior minister and then finance minister under President Jacques Chirac. (Chirac was convicted in 2011 on corruption charges tied to his time as Paris mayor.)
Ten days after his runoff election win, Sarkozy became president in 2007.
He served in that capacity for the next five years, garnering praise for his work on foreign policy issues and criticism for his handling of domestic issues as France's economy sputtered and unemployment rate hovered at about 10%.
In May 2012, Francois Hollande beat Sarkozy in his bid to win a second term as president.
And just over two months later -- one day after he and his family were set to head off to Canada for a vacation -- police raided his home and office as part of their investigation into possible illegal campaign financing, according to Herzog.
"It's not a surprise," Christian Mallard, a senior foreign analyst for France Television, said at the time. After losing his re-election bid, Sarkozy "was going to lose his diplomatic immunity," opening him up to potential prosecution.
In fact, the probe appeared well under way by then. In September -- when Sarkozy was still president -- three investigators engaged in an hourlong search of his political party headquarters, seeking documents linking his campaign to the alleged political contributions from Bettencourt.
Judge Jean-Michel Gentil questioned the former French leader in November for 12 hours concerning evidence given by Bettencourt's former accountant, Claire Thibout, BFM-TV reported.
Afterward, authorities said they'd decided not to pursue a formal investigation of Sarkozy, but rather to treat him as what officials call a "witness-under-caution."
The phrase is a technical term that essentially allows a French magistrate to continue to call the ex-president to the witness stand. At the same time, it didn't close the door to Sarkozy facing criminal charges stemming from allegedly illicit campaign donations.