Philip Cairns went missing on October 23, 1986, when he was 13-years-old, while making his way to Coláiste Éanna in Rathfarnham in Dublin, where he was a student.
His mother died suddenly but peacefully on Tuesday, surrounded by her family.
Ms Cairns was predeceased by her husband Philip. She was a mother of six, and had six grandchildren.
A funeral mass for Ms Cairns was held at the Church of the Holy Spirit in Ballyroan on Saturday.
Her son Eoin delivered a eulogy, telling mourners of his mother’s upbringing in Castlecomer, Co Kilkenny, where she grew up on a farm in a family of 10.
“Like many at that time, she came to live and work in Dublin where, at my aunt’s wedding, she would meet her future husband Phil,” he said.
He said his parents moved to Ballyroan when the family was still young.
Alice Cairns died peacefully on Tuesday, November 11. Photo: RIP.ie
Today’s News in 90 Seconds – Saturday, November 15
“And although she missed her old life, over time she made new friends and acquaintances, becoming more and more involved in the community.
“However, fate was to intervene with the disappearance of her beloved son Philip, and her life was to change forever.”
In the months that followed, he said Ms Cairns knew “this was to be her cross in life”.
“She accepted it, even if it was a heavy cross for her to bear. In all the while I knew her, never once did I hear her complain.
“I remember once she said to me that God never gives a cross to those who cannot bear it, and so knowing this, she accepted it with grace and dignity.
“But, she would also be the first to say that it was the support given to her and her family from her friends, neighbours, the whole parish, that made her cross that bit lighter for her to carry.”
Mr Cairns credited his mother for helping to bring happiness back into the family’s life after Philip’s disappearance.
“After all that had happened, what she wanted for our family was that life would return to normal.
“In time, the routine and humdrum of family life resumed and little-by-little, the happiness among the family slowly returned.
“It was in no small part thanks to mam, who even after all she went through, retained her curious sense of humour.”
He said Ms Cairns will be remembered for her faith, kindness and “gentle perseverance”, but he will miss her sense of humour the most.
Faith was the core of Ms Cairns’ life, he said, and “it was almost as if it was to be her mission in life to pray for others and to share, in her own quiet way, the joy she had felt”.
“She rarely spoke of herself, but when asked, she was happy to share her story of Philip’s disappearance, seeing in it a message of hope and trust that others would, maybe, find comfort it.”
Following the conclusion of the funeral mass, Ms Cairns was laid to rest in Mount Venus Cemetery in Rathfarnham.