We know that Joseph can interpret dreams. The chief butler knows that Joseph can interpret dreams, he just forgot about helping him out after being restored to his position in Pharaoh’s house. Then after Pharaoh has troubling dreams, that his wise men and magicians are no help with, the chief Butler is like “Oh yeah, now I remember…”

Genesis 41 

At the end of two full years, Pharaoh had a dream: and, behold, he stood by the river.