What is the evidence that lions were the symbol of royalty? In medieval heraldry, all sorts of armigers bore lions (it was the most common animate charge west of Germany, and near eagles east of that area).

The Aberdeen Bestiary describes the lion first and has things like "For the Greek word for lion is translated 'king' in Latin, because the lion is the king of all the beasts." But that rather seems to me that royalty was the symbol of the lion, so to speak.