Asriel froze.  Twilight's dust sifted through his claws like sand.  He didn't move.  Tears formed in his eyes.  His own daughter suffered the same fate he did, without deserving it.  She hadn't done anything wrong, yet the humans killed her... And in the middle of a truce. What would he tell her friends? What would he tell Frisk?

He was furious.  This could only mean one thing.

"This means war."  Asriel muttered to himself, clenching a pawful of Twilight's dust.  "I don't care what anyone thinks...  All I know is that our daughter is dead...  And there's no choice but to fight back."

His words were overheard.

"ASRIEL DREEMURR!!!"

He froze and turned around to see Frisk glaring at him angrily.  "What in the name of Asgore do you think you're doing!?"  they snapped.  "We do not need to declare war!"

Asriel glared back.  "The humans killed Twilight!  We have no choice!"  he shouted.  Frisk hesitated.  "...  Just because they killed her...  Doesn't mean we need to declare war again.  You're going to get us trapped back underground!  Think of all the lives it would cost!" 

He didn't listen.  All he wanted was revenge.

And so the war was fought.  Lives were taken.  But what happened afterwards was the worst thing of them all.

Frisk was right.  The monsters had lost again.  The humans were ready to seal them back underground...  And they did.  But what they didn't realize...

There was still someone left.

And that special someone would change everyone's lives forever.

That someone was the lost princess.