be first/second/next etc in line to the throneto be the person who has a right to become a future king or queen 是王位的第一/第二/下一位等继承人 As the eldest son, he was next in line to the throne. 作为长子,他是王位的下一位继承人。
→ be first/second/next etc in line to the throne at line1(11)