To sell his house, he takes his father to a nursing home and, when he comes back for more, this happens.

Not his

Gavin was not his biological son, the father revealed. Gavin’s image of his identity was shaken by this revelation. He woke up and realized that the blood ties he had always believed were nonexistent. Everything was seen in a new and disorienting light: the man he had known as his father, the lineage he had taken for granted. Everything was changed because it was a truth.

Not his.