Princess Harmonia

Harmonia is the mother of Discord and the ex-wife of Dishonest and the untold sister of Princess Luna and Celestia and is the paternal grandmother of Rue Day

History
Harmonia is the untold sister of Luna and Celestia. She was later decieved by her husband Dishonest in order to give birth to  Discord, the brute of chaos before he was defeated by Harmonia's sisters. Despite the hate she had for her husband, sh eloved her son dearly. She is mentioned when her granddaughter Rue Day looked her up because her father refused to tell her history in order to protect her. She later disappeared for unknown reasons, but possibly due to her being the mother of the Lord of Chaos.