I have decided to give toi all Moon Dust's back story so enjoy and comment!
Moon Dust was born on Hearths Warming Eve. Her father was a pegasus named arbre Whisper. Nopony knew who her mother was. Moon Dust was delivered onto her father's house the night she was born par Princess Luna.
Luna a dit she found Moon Dust in the snow par the château with a note telling the princesses he was her father. Luna a dit she sensed great power from this filly. arbre Whisper asked her to name the filly because naming the filly was not his job.
Moon Dust was named Moon Snowy Dust Moon Dust for short. arbre Whisper raised Moon Dust until another filly with a arc en ciel mane was delivered to his house with a name and note saying she was named arc en ciel Wing. par then Moon Dust was 2.
When Moon Dust was 10 she was accepted to Celestia's School for gifted licornes and when she turned 12 she was made Luna's apprentice.
So that is most of Moon Dust's back story