Sister Armor by ~dm29 on deviantART

Cadance: “Twilight, I’m sorry but this was all my fault. Three days ago, I was working on something to enhance the Crystal Heart’s power but it didn’t turn out so well (speech gets more flustered) and Shining Armor here got hit and now my husband is a filly, Twilight. (shakes Twilight some more) THE CAPTAIN OF THE ROYAL GUARD IS A FILLY.”