look up any word, like darude - sandstorm:
 
1.
1) Your girlfriend is cheating on you.
2) She ain't here.
3) You tried really hard, but you failed.
4) You just got pwned by either Princess Peach or Princess Daisy.
1) Guy: I thought she was mine, but it looks like the princess is in another castle.

2) Guy 1: Where is she?
Guy 2: The princess is in another castle.

3) Graduate student: I tried to get my doctrate approved, but the it looks like the princess is in another castle.

4) Princess Daisy: I'll just be flying under this plane over here.
Young Link: (Dies)
Princess Daisy: The princess is in another castle!
by TheWizardof207 March 07, 2004
 
2.
1) The event in which you expect a female, only to get something else (like a dude) instead, especially in the case of dating a transvestite or someone similar. The phrase originates from Super Mario Bros., where instead of getting the princess at the end of all but the last castle, you end up rescuing a Toad instead.

2) The event in which a female does not show up at the appointed place and/or time.
Male 1: "Dude, I went out with this one bitch, only to realize she was really a guy!" Male 2: "Haha, the princess is in another castle!"
by Ilikesex12 December 14, 2009