Alicorn Pony who is first featured in the season two finale A Canterlot Wedding - Part 1 alongside Shining Armor, her husband (after the season 2 finale). She is Twilight Sparkle's foal-sister in Twilight's flashback, and she became her sister-in-law after marrying Shining Armor in A Canterlot Wedding - Part 2. Various promotional materials, including a New York Times ad, A Canterlot Wedding - Part 1's Hubworld, iTunes, and Netflix summaries, the back cover of the Royal Pony Wedding DVD , and the home page of Treehouse TV's Royal Wedding Contest site, state that she is the niece of Princess Celestia , and the chapter book Twilight Sparkle and the Crystal Heart Spell specifies that Celestia adopted her as a niece.
A blurb on one of the toy sets featuring Cadance says that she and Shining Armor "lead the Crystal Empire together!" Indeed, a background pony proclaimed her as "The Crystal Princess!" at the end of The Crystal Empire - Part 2 .