Sunburst was the official crystaler. It was his job to help care for the young princess, and he had grown used to and even enjoyed the task. It was a pity, if one asked Flurry Heart, that he lacked a little trait that'd make him the best foalsitter.
When Starlight approaches Sunburst the night before he returns to the Crystal Empire, she inadvertently discovers something about her old friend that explains a bit about their past—and present.