On the evening of April 15, Olivier Latry, one of the world’s greatest organists, arrived at a hotel in Vienna ahead of a planned concert.

“I had just put my luggage down and received a text,” he said in a telephone interview. “It was from a friend, and it just said, ‘Notre-Dame is burning!’ and there was a picture of the roof on fire.”

“I could not believe it, of course,” he added. “But then a second picture arrived …” He trailed off. “It was like a bad dream.”

A day earlier, Mr. Latry — one of the three main organists at Notre-Dame — had played the cathedral’s Grand Organ on Palm Sunday. It had been a beautiful service, he said, especially the moment when, according to tradition, a priest knocked on the cathedral’s door with his processional cross and demanded to be let in.