As Grisey's new girlfriend, Mireille Deguy became an essential part of his family life. When Raphaël was going through a tough phase as a teenager, he came to stay with them. Deguy fell into the role of disciplinarian by default. “Gérard wasn't able to be firm with his son because he felt guilty for leaving him when he was small,” she said. Raphaël recalled that he and his father had their “first real conversations” at this time. But Grisey didn't pass his love of classical music on to his son.

Like France Detry, Deguy also went to visit Lucie Monna, Grisey's mother, with him. She remembers the house as having a small interior but a large garden. They only went into the town of Belfort once; Grisey preferred to walk around the small hills, forests, and ponds by the village of Chèvremont. They enjoyed the view of what Alsatians call la ligne bleue des Vosges, the silhouette of the mountain range that separates the region from its neighbors. Deguy recalls that in this time, Grisey was thinking of leaving Paris for a place in the country, a desire strengthened by the time spent in the natural environment of his childhood home.

Like Detry before her, Deguy picked up on Monna's strictness. She realized Grisey and his mother couldn't interact on an intellectual or musical level. In photographs from these visits, Monna is as well put together as always, her clothes and her hair orderly, but her gaze is a little slack. In about 1995, Monna began to suffer from dementia. One day, she had a stroke and fell. Grisey felt he had no choice but to bring her to a nursing home, though he did so unwillingly. Claudia Doderer remembers Grisey calling her after a visit to the home in Belfort, shocked and sad, and saying, “Claudia, now I understand how the world works.”

According to Deguy, life in the nursing home was too difficult for Monna and she died after only six months. “In spite of everything, he was close with his mother,” Deguy said. To process his loss, Grisey began reading texts by the ancient Tibetans, Greeks, and Romans on death, and planning for the composition of Quatre chants pour franchir le seuil. In 1962, at the age of sixteen, Grisey had composed his first piece for his mother, the Petite Caprice en La.