Paul Cantlie, who recorded a video message from hospital after undergoing throat surgery earlier this month, died on Thursday from complications following pneumonia, the family said.
The family had repeatedly tried to get messages to those holding Mr Cantlie. “Paul died not knowing whether John’s captors had received any of the messages he had sent to them," a statement released on Tuesday said. "The failure of communication to date has inevitably led to a terrible sense of abandonment, particularly for John’s father, with the family feeling ignored."
It added: "This burden has been especially hard these last few days, as we have so needed to tell John that his father, whom he so loved, has died.”
In a video filmed by the BBC on October 3, his 80-year-old father, who was undergoing treatment for a chest infection after an operation to remove his voice box, told his son's captors: "Speaking entirely for myself, this is not how I had imagined I would be passing my 81st year.
"I want John to know how very proud I am of him. I can think of no greater joy than seeing my dear son released and allowed to return home to us."