How to marry a sim when bethroed to another

Question

Hi. Im doing the quest to get allies with Effenmont(A political marrige). And im supposed to marry the princess. The problem is that my sim is already engaged to another sim, witch i cant seem to break up with, because she has dissapeard(I think she was a part of another quest and when it ended, she dissapeard with it). Is there any cheats so that i can change theyre relationship, whitout finding the sim?