Princess Cadence

She is Twilight's former foal sitter and current sister-in-law. She is married to Shining Armor and has been referred to as the "Crystal Princess". Her cutie mark is a crystal heart.

Princess Cadence is the daughter of Princess Luna.

The color gradient in Princess Cadence's wings is from an illness.

Queen Chrysalis wanted to immitate Princess Cadence because Princess Cadence was going to rule over the Crystal Empire, which is powered by love, and would therefore be a large resource of food for her and her subjects.

Rarity is secretly Princess Cadence.

Twilight Sparkle is now the Princess of Friendship, as Princess Cadence is the Princess of Love