You walk into the throne room and encounter Asgore. He questions what monster you are then you kill him. After you kill Flowey you answer Asgore's question with The Angel of Death.
You go to the ERASE button to complete the task that you were made to do. But blue magic takes you away from the button at the last second. You turn to face the monster that stopped you from ERASING this stupid world and you recognize a familiar comical grin with two blue glowing eyes.
Then you suddenly start to fall. As you fall again you see a skeleton like figure but he has two cracks coming from his eyes and looks faded.
A split second later he disappears and you see the golden flowers one again.