The actor Sam Neill, whose death on Monday at the age of 78 prompted an outpouring of grief and tributes in his home country of New Zealand and around the world, died from pneumonia, his longtime agent said in a statement.

Mr. Neill had “valiantly fought and beaten” lymphoma before he became sick with pneumonia, said Philip Grenz, his agent of 19 years. Mr. Grenz said he was releasing the information to dispel inaccurate reports about the cause of the actor’s death.

Mr. Neill was diagnosed with angioimmunoblastic T-cell lymphoma in March 2022, but was cancer-free at the time of his death after receiving treatment through CAR-T therapy, Mr. Grenz said in the statement.

CAR-T is a novel immunotherapy treatment that involves removing a patient’s T cells, white blood cells that fight viruses, and genetically engineering them in a lab to fight cancer before infusing them back into their bloodstream.

Mr. Neill first disclosed his cancer diagnosis in his 2023 memoir, “Did I Ever Tell You This?” After the release of the book, he told The Guardian in an interview: “I’m not afraid to die, but it would annoy me. Because I’d really like another decade or two, you know?”

The actor will be honored with a private memorial at his farm in New Zealand’s Central Otago region “as Sam was an intensely private man who loathed a fuss,” his agent said.

Four projects that Mr. Neill had filmed back to back last year are scheduled to be released in the coming months, according to the statement.

Mr. Neill was mourned in the small communities in the South Island of New Zealand where he lived, and locals said he carried himself as “a regular bloke.” Scores of actors and directors who collaborated with him on more than 150 films and TV shows also praised his talent and how much of a joy he was to work with.

“He showed me the depths of loyalty, protectiveness, and love, always with the driest of wit,” his “Jurassic Park” co-star Laura Dern wrote in an Instagram post. “He was a true and noble gentleman, wrapped up in my dream leading man.”