Jack Doyle Snr, whose daughter Elaine, 16, was also brutally murdered in Greenock, spent 25 years campaigning to bring her killer to justice.
And last week, the family began a second campaign after Jack died not far from where Elaine's body was found in 1986.
Jack Snr passed away in Greenock's Ardgowan Hospice before seeing anyone brought to justice for the murders of his grandson or daughter.
The 69-year-old, who is survived by his wife Maureen, had been suffering from cancer. The family have gathered at their Gourock home to mourn their latest loss.
A murder hunt was launched on Tuesday after young Jack was found dead near flats, in Hope Street, at 9.45am.
The discovery was made less than two miles from the lane off Ardgowan Street where his aunt's body was discovered 25 years previously and just months after police opened a cold-case review into Elaine's death, which remains unsolved. The teenager's dad, John, 47, was Elaine's older brother.
Police hunting both killers say the inquiries are not linked.
In June, Jack Snr spoke out on the 25th anniversary of Elaine's death. He said: "We have never given up hope that one day our questions would be answered. We deserve justice."