What was the Greek name of Cleopatra's son Alexander Helios' twin sister?

Alexander Helios' twin sister was named Cleopatra Selene, more fully Cleopatra Selene II. Her name forms a deliberate pair with her brother's: Helios means “Sun” and Selene means “Moon” in Ancient Greek.

Cleopatra Selene was born around 40 BC to Cleopatra VII of Egypt and Mark Antony. She and Alexander Helios were fraternal twins, not identical twins, and were publicly acknowledged by Antony in 37 BC. Their names connected the children to both royal and cosmic imagery, presenting them as heirs in a grand Ptolemaic-Antonian political program.

At the Donations of Alexandria in 34 BC, Antony and Cleopatra assigned impressive titles and territories to their children. After their parents' defeat and deaths in 30 BC, the twins were taken to Rome and raised in the household of Octavia, Antony's former wife and Octavian's sister.

Cleopatra Selene later married Juba II of Mauretania and became a significant royal figure in North Africa. “Selene” is the key identifying name; it should not be confused with Arsinoe, Tryphaena, or Berenice, other women of the wider Ptolemaic world.