What is the relationship between the two children when a man marries a woman, and his son marries the mother of that woman?

Primary text

When a man marries a woman, and his son marries that woman's mother, the resulting children from these unions share a specific kinship: one child is the paternal uncle (amm) to the other, and the other is the maternal uncle (khal) to the first. This principle was affirmed in a narrative involving Al-'Uryan ibn al-Haytham.