Who played a joke on wei li by Xing Dongdong in Biography of Mao Zedong? Who can tell me the complete joke?

Several years ago, you married a widow. The widow has an adult daughter. Became your daughter, and later your daughter married your father. She became your father's daughter-in-law and your stepmother. Your father became your son-in-law. Two years later, your wife gave birth to a son. He is your stepmother's half-brother. Your son calls you dad, and you call your son uncle. Later, your daughter also gave birth to a son for your father. Your brother, but he has to call you grandpa. You are your wife's husband. Your daughter-in-law is also the mother of your stepmother, that is, your grandmother. Now the problem is coming. What are you?