He had a son with Cleopatra

Caesar traveled to Egypt in 48 BC to find the Roman general Pompey, one of his rivals. While there, he encountered Cleopatra who was engaged in a civil war with her younger brother and fellow monarch Ptolemy XIII (per ancient Egyptian custom, the two ruled under the formal title of husband and wife). Caesar asked the couple to come to meet him so they could settle their dispute after announcing himself as the father of the siblings' siblings' executor of the will. Some tales claim that Cleopatra slipped herself into a laundry bag to meet Caesar for the first time after Ptolemy's army prevented her from going to the palace where he was staying. Roman general Caesar and Cleopatra, who was half his age, fell in love. Around 47 B.C., Cleopatra gave birth to Ptolemy Caesar, a boy who was thought to be Caesar's offspring. He was known as Caesarion, or Little Caesar, by the Egyptians.

Ptolemy XIV, Cleopatra's brother, and the fellow king were assassinated not long after Caesar was killed in 44 B.C. (Ptolemy XIII, her former co-regent, had passed away around 47 B.C.) Although it was never verified, there was a rumor that Cleopatra poisoned Ptolemy XIV to anoint Caesarion as her co-ruler the following year. He adopted the name, Ptolemy XV.