John and Ethel May would raise the baby as their son. June would be presented as the older sister. The child would know nothing different because there would be nothing different for him to observe. He would grow up with a mother, a father, a couple of older sisters, a normal domestic situation — and the fact that one of those sisters was biologically his mother would be a fact that only the adults would carry.
Jack Nicholson grew up with this as his reality. Not a performance. Not a secret he was excluded from. A reality. He called Ethel May “Mom.” He called June “sis.” He called John Nicholson his father. These were not performances of family relationships; they were the relationships, the only ones he knew.
When June died of liver cancer in 1963, Jack was twenty-six. He mourned her as a brother mourns a sister. When Ethel May died in 1970, he was thirty-three, by then a working actor in Hollywood with a decade of bit parts and near-misses behind him. He mourned her as a son mourns a mother. He had no frame that suggested he should feel anything other than what he felt.
The phone call in 1974 did not change what he had felt. It did not retroactively transform grief into something else or love into something different. What it changed was the label. The relationship he had experienced as one thing was now understood to be something else. The woman he had mourned as his sister was his mother. The woman he had mourned as his mother was his grandmother. The feelings were the same. The understanding of them was now different.