If met an disney princess e.g. Rapunzel at the princes pavilion can ask to meet and different princess.
You only see one of the 2 who are available on the visit. Sometimes they ask if you have seen anyone already and if you say yes and they are one of the 2 there the cast member will try to put you in the other queue.
We went with my daughter and she was dressed as Rapunzel, we didn't know but they had lined us up for one princess but the other princess was Rapunzel herself. The 2 CMs spoke to each other in French then mouthed to me, did she want to meet Rapunzel? I said yes so they swapped us over (it's only at the very end you get put in front of one door or the other).