Simplify the following text for a Grade 3 native English-speaking person.
Original: In Greek mythology , Helenus ( á 1\/4 Î '' Î Î 1\/2 Î Ï ) was the son of King Priam and Queen Hecuba of Troy , and the twin brother of the prophetess Cassandra .
Simplified: Helenus was the son of King Priam and Queen Hecuba of Troy . His twin sister was Cassandra .