Reference for Zevachim 203:5

קתני מיהת יבמה מלך מלך אין כ"ג לא אימא אף מלך

and her brother [Nahshon] was the prince of his tribe; yet she was bereaved of her two sons. At all events he teaches, Her brother-in-law was a king: thus he was a king, but not a High Priest? - Emend, was also a king.

Jastrow