Real Originals fans, how did Mikael and Esther show up in Vampire Diaries and the beginning of Originals it was like nothing happened in TVD? How did Mikael come back to life and appear in Originals if he really died with the white oak stake in TVD?

How come in the Originals, it was like a total surprised to them when Esther showed up, like she hasn't been alive since the very beginning when Klaus killed her but she was already in TVD? I don't watch TVD and only a fan of the Originals but many ppl suggested if you want to know more about the Originals history, watch TVD. Watching a few esp is making me more confused and filled with questions.