It was supposed to be a formal visit. The Princesses would come, say somethings, and leave. But during Celestia's speech, somepony turned Luna into a target. Before the Princesses could even blink the guards had tackled a pony in the crowds, and a stallion lay dying at Luna's hooves, whispering his last words into his young daughters ear. Then His last breath escaped him, leaving his daughter to cry over his broken body, leaving her alone in a cruel world. And Luna feels responsible.
What happens next? Only time will tell. But I can tell you, that both their lives, will be affected greatly.
[This is not part of the Familyverse.]
{I got rid of the Tragedy tag, because there was only one tragedy and I suck at making sad things. I might put the Tragedy tag back up if I fit in another terribly incident, which I'm not saying I will, but I might.}