An internal probe established that a 2016 sponsorship deal with the Chateau de Versailles included a 50,000 euro (£44,022.2) personal benefit to Ghosn, the carmaker said on Thursday, confirming a report in Le Figaro.
The carmaker replaced Ghosn on Jan. 24, more than two months after his arrest in Japan over allegations of financial misconduct uncovered by Renault's Japanese affiliate Nissan, which he also chaired.
Renault began its own examination of payments to Ghosn within days of his detention but had not flagged any irregularities until now.
"The event space at Versailles was made available to him without charge, and Mr Ghosn was unaware that the use of the space would be charged against Renault's allotted usage," Ghosn's French-based lawyer Jean-Yves Leborgne said in an e-mailed statement.
"Carlos Ghosn paid for all of his wedding expenses," he added.
Renault has discovered that "Mr Ghosn was accorded a personal benefit valued at 50,000 euros under the terms of a sponsorship contract with the Chateau de Versailles", the company said in a statement on Thursday.
"Renault has decided to bring these findings to the attention of the judicial authorities."
The office of Ghosn's Japanese lawyer, Motonari Otsuru, did not immediately respond to a request for comment. Ghosn remains in detention in Tokyo with limited opportunity to respond publicly to allegations against him.
Renault had agreed before the wedding to sponsor 2.3 million euros of Versailles renovations in return for a credit granting the carmaker services from the chateau worth 25 percent of that amount, or 575,000 euros, a person with knowledge of the matter told Reuters.
The rental fee was deducted from Renault's credit for use of the Grand Trianon at Versailles on Oct. 8, 2016, when Ghosn and his second wife, Carole, hosted their wedding reception at the 17th-century palace, the source said. The event had already attracted public attention for its opulence and Marie Antoinette-themed costumes.
The Renault board was informed about the discovery on Wednesday, as reported by Le Figaro, the source added.
(Reporting by Laurence Frost; additional reporting by Tim Kelly in Tokyo; editing by Keith Weir and Stephen Coates)