I just had a minor brainwave... Probably stating the obvious here, but the mysterious tablet is adorned by the arms of Sahkmet, so it's most likely NOT a qasalan tablet...

However, since the prince seems to be a 1000 years old, and it seems he's tried getting married in Sahkmet before and was stumped, perhaps this tablet (which might be equally old) gives a clue on how he was defeated before and therefore how he can be defeated again?

Just a thought :P