My boy is named Castor.
Pollux (or Polydeuces) and Castor are the names of the constellation Gemini according to Greek mythology.
They had different fathers although they were twins – the father of Pollux being Zeus making him immortal.
When Castor lay dying after a battle Pollux begged Zeus to allow him to die with his brother. Instead Zeus allowed them to share Pollux’s immortality.