Prince of Darkness and Princess of Mewni

I don't own Star vs the forces of evil (What a shocker!)
An AU based on a theory/idea that as far as I know has only been thought of by me and I'm probably the only one who wants it to be true. Marco is actually Mars Butterfly the younger yet stronger brother of Meteora Butterfly and the only son of former Queen Eclipsa. A natural with magic Marco has been living with his constantly on the run dad for around fourteen years he is suddenly caught and crystallised alongside his mother or being too big a threat to Mewni, his father disappears from everything out of grief and is presumed dead. Many years later Star a kind and energetic princess is fourteen and is getting the family wand but what happens when a complicated set of circumstances lead to her setting free Mewni's greatest fear?