Crowds of visitors were cleared out of Notre Dame Cathedral in Paris on Tuesday when a man put a letter on the monument's altar before committing suicide by shooting himself in the head.
Monsignor Patrick Jacquin told the Associated Press that this is the first suicide the landmark church has seen in decades.
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"It's unfortunate, it's dramatic, it's shocking," Jacquin said, adding that a few people have committed suicide by jumping from the cathedral's twin towers, but that he had never heard of anyone committing suicide on the altar.
Local media reports said he was a 78-year-old writer and essayist.
French website Europe1 has identified the man as Dominique Venner, a former member of the Secret Army Organization (OAS), which opposed Algeria's independence in the early 1960s.
Venner was also known to be opposed to France's recent decision to legalize same-sex marriage, which President Francois Hollande signed into law on Saturday.
Notre Dame was closed to the public as police investigated the incident. It is very rare that the cathedral, visited by around 13 million people each year, is evacuated.
This year marks the 850th year since Notre Dame's construction began, with the cathedral getting new bells as part of the celebration.