Adam's mum, Jackie said Harry Robinson had been well, but less than 48 hours after learning of his 20-year-old grandson's death, he was dead.
Jackie and Martin Chadwick, whose son was gunned down by a masked gang in what police believe is a case of mistaken identity, said they were convinced the murder was too much for the 70-year-old to bear.
Today detectives are hunting Adam's three attackers who, accompanied by a mystery woman, burst into his sister Gemma's terrace house in Clifton Mount, Harehills, Leeds, and shot him at 10.20pm on June 24.
Mrs Chadwick said that despite suffering from cancer her father had been well.
Mr Robinson, a retired miner from Castleford with seven grandchildren and two great grandchildren, had tried to put on a brave face over the tragedy.
Mrs Chadwick, of Seacroft, Leeds, said: "I spoke to dad again on the Friday (June 27]. He said: 'Don't worry about me. You have to do what you have to do. Don't worry, I will be fine, I will be strong.' But I know he was fretting about me and us all."
He died of cancer on Saturday.
Martin Chadwick told the YEP: "Adam and his grandfather had enjoyed the same cheeky humour and frank approach to life."
Mr Robinson worked at three mines including Featherstone before running a boarding house in Bridlington. He returned to live in Airedale, Castleford.
His funeral will be at Lawnswood Crematorium, Leeds, at 1.40pm on Tuesday.
The man leading the hunt for carpet fitter Adam's killers, Det Supt Steve Payne, said it was vital the mystery woman, pictured, who had earlier called at the house in Clifton Mount enquiring about a 'Michelle' contact police. He told her: "I urge you to come forward now, before we coming knocking on your door."
Today Adam's school, Wortley High, paid tribute to the popular pupil and talented soccer and rugby player. A school spokesman said: "Adam is remembered by staff as a popular and pleasant pupil who always had a smile for everyone."