In this AU, Sombra wasn’t defeated during the first Crystal Empire attack. Due to the events that took place (I’m still working out the details), he was forced to take a partner to keep his status as King and to regain his full power. After all, a King needs a Queen, right?

Diamond had taken a trip with her family and to the Crystal Empire to celebrate its sudden return, and Sombra’s subsequent arrival took everypony by surprise, locking them in the Empire and keeping them from escaping back home. The magic he used to regain his power was finicky and had a number of conditions. He couldn’t marry a Crystal pony. He couldn’t break up a marriage. He couldn’t mind control a pony to agree, and she would have to say yes of her own free will.

Diamond Tiara’s parents were (somewhat happily) married, so Spoiled Rich wasn’t an option, nor was Filthy. Cadance and Shining Armor were married, that wasn’t a possibility either. There were no other non-Crystal ponies in the kingdom, so…Well, he didn’t want to marry some spoiled brat, but he had no choice. Mind control wasn’t allowed, so it took a lot of convincing, threatening, bribery, and sugar coating to make Diamond agree to the deal. It was a bit more threatening than anything else, but that’s a bridge we’ll burn when we get to it.

He actually did his best to make the wedding nice. He got together a crowd (in chains), had his fiancee prettied up, he put on a suit and tried not to snarl at her through the ceremony.

It was…extremely uncomfortable.

But it happened! Now Diamond and Sombra have a binding marriage and he can’t just ditch her because, would you look at that, more conditions that he would need to obey! Dang Sombra, you really dug your own grave.