In written history, Commodus's only family member after he inherited the throne was his sister, Lucillia. But this did not mean that he had no other siblings. In fact, Aurelius had many children, but most of them failed to reach adulthood. And eventually, only two children were left after his death.
If Aurelius's dead children were included, Commodus was supposed to have many brothers. And among them, the one closest to Zhang Heng's age was Commodus's twin brother who died at the age of four. Aurelius held a funeral for him, and the Senate stopped working for a day to express their grief.
The ordinary citizens in the city of Rome still remembered it fondly until today.
As far as everyone knew, Commodus's twin brother had indeed passed away.
