There're 3 level of "Chao Fa" (the highest rank of King's son or daughter is "Chao Fa")
"tul-ka-mom" refer to first class Chao Fa, "Som-det" refer to second class Chao Fa, I forget about the third one.
Although Princess Ubolratana is not officially Chao Fa, but most of thai people still call her...