You and Klaus were close as kids. You two were inseparable. You protected Klaus no matter if you got hurt or not, Klaus protected you, which made him fall in love with you, then you disappeared. You were gone for years. Now he's 1074 years old (cause he's a hybrid so he lives forever), and you're 1073 (also because you're a hybrid and can live forever). You end up on the front door step and Elijah answers the door. Once he sees you, he shouts for Klaus Elijah: Klaus! You have company!

Klaus: I don't care, it's not-...

Klaus looks at you and his walls crumble.