What is the status of the child born to the female slave after the father has intercourse with her, given the son had prior intercourse?

Primary text

If the father has intercourse with his son's female slave, and the son had intercourse with her previously, the child born from the father's act is freed by reason of kinship (*dhū rahimin*) to his brother (the son's other children or the son himself, depending on context implication, but the immediate ruling is freeing the child to his brother).