(CNN) -- It was a promise the castaway made to a dying man: He vowed the man's mother would learn how he perished and hear his last words.
Jose Salvador Alvarenga flew from El Salvador to Mexico this week to keep his word -- more than a month after the stunning story of his survival at sea captured international attention.
"It's a promise that we both had made," Alvarenga said after landing in Mexico City, "and now I'm here to fulfill it."
Alvarenga was found in an atoll in the Marshall Islands in late January. He told authorities there he had drifted on a small fishing boat for 13 months all the way from Mexico, more than 6,000 miles away.
As some hailed what seemed to be his miraculous survival and others said they doubted his story, there was a tragic side to the tale. His traveling companion, fellow fisherman Ezequiel Cordoba, 23, hadn't made it.
Alvarenga said Cordoba had died four weeks into their ordeal because he couldn't manage to drink turtle blood and eat raw fish.
This week, they got some.
Roselia Diaz, Cordoba's mother, said she was grateful that Alvarenga had traveled to the coastal Mexican town where she lives.
"For me, it would have been sadder if both had died, because I never would have known what happened to my son," she said. "So I'm very happy to see him again."
Alvarenga told reporters that Cordoba often spoke about his mother.
"He told me a lot about her, that she was a very good person with everybody, and that she was very loving," he said.
Alvarenga also told Cordoba's mother how the two fishermen passed the time while drifting in the open sea.
Cordoba, an Evangelical Christian, told the Salvadoran fisherman about his faith as they both clung to the hope of being found alive and rescued in the middle of the Pacific Ocean.
"He taught me how to pray," Alvarenga said. "He taught me to sing."
The castaway said there were some things Cordoba told him that only the dead fisherman's mother must know.
"To reveal them publicly," he said, "would be to betray his memory."
CNN's Nick Parker and Catherine E. Shoichet contributed to this report.