אפשר עזרה ממכם בחידה באנגלית?! פירוט בתיאור

A father and his son are in a car accident. The father dies instantly, and the son is taken to the nearest hospital. The doctor comes in and exclaims, I cant operate on this boy.

Why not? the nurse asks.

Because hes my son, the doctor responds.

How is this possible?