Answer:
Take one royal word in the plural and make it singular by adding one letter
What you become during a workout?
What kind of nail can be grown?
Four kings of whom I am one lord. Often on deck but never on board. Though I have a large heart, I am always seen at war. During which I always wear a suit, but never a suit of armor. Who or what am I?
What grows when it eats, but dies when it drinks?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?