A Dallas man caused a fright at the opera Saturday when he strode up to the front of the theater during intermission — and scattered the ashes of his beloved dead friend inside the orchestra pit, police said.

The bizarre, only-in-New-York moment happened during the second intermission at the matinee performance of “Guillaume Tell—’’ when jeweler and opera buff, Roger Kaiser, 52, paid his friend a final, musical tribute, sources told The Post.

“Oct 29 is gonna be a good day!” Kaiser had posted on Instagram, as he posed with his tickets for both Saturday’s matinee and evening operas — what he termed a “#doubleheader.”

“I am exited,” he posted on Facebook, above a snap of himself with an apple on his head — a la William Tell.

But while the moment may have been special for Kaiser, it hit a sour note for the rest of the audience.

The end of the show was canceled, NYPD counter-terrorism cops rushed to the venue and samples of the ashes — described as a “white powder’’ — were collected for testing.

Most of the audience had not even seen what happened, instead learning of the trouble upon taking their seats after a longer-than-usual intermission.

They saw an empty pit, and an announcement was made that the performance had been canceled due to “technical’’ problems.

The Met employee delivering the bad news was greeted by shouts of “No!’’ and, ”I want my money back!’’

One of the people demanding a refund kept screaming until members of his fed-up audience told him to shut up.

Kaiser quickly left the theater. But members of the audience, to whom he’d confided his ashy mission, fingered him to cops.

When authorities caught up to him, Kaiser admitted that he came to the opera to “sprinkle the ashes of his friend and mentor’’ who “loved the opera,” a law-enforcement source told The Post.

Authorities said Kaiser might not face criminal charges as long as the “powder’’ proved to be what he said it was.

Officials were searching through the city’s administrative code to see what charges, if any, he could face.

“At this point, I don’t think we would refer to him as a [crime] ‘suspect,’’’ John Miller, NYPD deputy commissioner for intelligence and counterterrorism, told reporters.

The evening performance of “L’Italiana in Algeri’’ — for which Kaiser also had tix — was also canceled.

“My viola case (black cover) is still in the pit,’’ Met violist Vincent Lionti lamented on the orchestra’s Facebook page. Another musician joined in: “As are all our instruments.’’

Additional reporting by Shevarnanzi Calle and Ely Cepin