When Fancy and Rarity separated finally, Rarity was hesitant to get into another relationship. She was worried how anyone would treat her kids. One day Apple Jack and Big mac were helping Rarity move her stuff back to ponyvill, Big Mac having gone through his own separation supported Rarity through her's.

And though Rarity was starting to feel feelings for Big mac, what sold her was his bond with Clear Crystal. He took to her pretty quickly and even treated her like his own, Apple Fritter and Clear became close as well. It was a natural transition with their relationship. Rarity didn't think she'd remarry, but before you knew it the two were marrying a few years later.

Having their own kids together, yet Rarity's two from Fancy were still a big deal in big mac's eye.

Both of Rarity's kids call Big mac dad, and he lets Clear model him and they even would have tea parties together.

Even if they're not blood, Big Mac loves his kids. All of them. Regardless of who their father is.