In this world, Spike is of adolescence and through altering of timelines, he is a mid-adolescent dragon by the time he meets Rarity for the first time.
Rarity and Spike hit it off a long time ago. It was love at first sight, and while Rarity wasn't exactly stricken with love at the first sight of this dragon, he sure knew how to woo her. The results were a very successful relationship. In fact, they married over the subject of Rarity and her sudden pregnancy.
However, apparently some ponies consider this taboo. Destruction ensues.