It was a return to the stage that some feared would never happen again.

Last year the beloved Russian baritone Dmitri Hvorostovsky withdrew from staged opera — including a run of “Eugene Onegin” performances at the Metropolitan Opera — because of a brain tumor. When it opened without him, the soprano Anna Netrebko and the other members of the cast held white roses during their ovations in tribute.

But Mr. Hvorostovsky made a surprise return to the Met on Sunday night, and his performance became the emotional high point of an all-star gala concert — and the payoff of a plan that had been quietly set in motion less than two weeks earlier.

It was Mr. Hvorostovsky’s success at an April 25 concert in Toronto — where he appeared alongside Ms. Netrebko, his longtime friend — that led Peter Gelb, general manager of the Met, to invite him to appear at the company’s gala celebrating its 50 years at Lincoln Center.

“The concert went very well, and a few days later I spoke with him when he was back in London,” Mr. Gelb said. “He told me that his doctors encouraged him to keep singing, and that every day he had been working out physically and singing every day, and he said he really wanted to come to New York and be part of the gala.”