Royal? It is the Levite cloth of a Hebrew slave.
4 seconds sound clip from the The Ten Commandments (1956) movie soundboard.
You can hear this line at 00:15:35.151 in the Blu-ray version of the movie.
Quote context
[...]
- Go on. Hurry up! You've hurt her enough.
- Your husband is in the house of the dead.
- And he has asked the Nile god to bring me this beautiful boy.
- Do you know the pattern of this cloth?
- If my son is covered in it, it is a royal robe.
- Royal? It is the Levite cloth of a Hebrew slave.
- This child was put upon the water to save its life from your father's edict.
- My mother and her mother before her were branded to the Pharaoh's service.
- I will not see you make this son of slaves a prince of Egypt.
[...]