What was the name of Alexander's son born after his death?

Alexander's son born after his death was Alexander IV. He was the posthumous son of Alexander the Great and Roxana, born in 323 BCE shortly after Alexander died in Babylon.

Alexander the Great left no adult legitimate heir. Roxana was pregnant when he died, so the Macedonian generals agreed that her child would inherit the throne if it was a boy. When the child was born, he was named Alexander and formally became king alongside Alexander's half-brother Philip III Arrhidaeus, who had significant disabilities and could not rule independently.

Alexander IV never exercised real power. The empire was controlled by competing regents and generals, first Perdiccas and later figures such as Antipater and Cassander. As the Successor Wars intensified, Cassander had Alexander IV and Roxana secretly killed at Amphipolis around 309 BCE. He is sometimes confused with Heracles, another son of Alexander the Great, but Heracles was born to Barsine and was not the posthumous heir recognized by the Macedonian army.