#1 Brock Lesnar at WrestleMania XXX
Brock Lesnar was the one who finally managed to end The Undertaker's unbeaten streak at WrestleMania. However, the Beast Incarnate did not want to break the streak, and it was the sole decision of Vince McMahon that made things happen.
JR and Shawn Michaels confirmed the rumor later on, while Paul Heyman also hinted at it when asked a little later. The Undertaker was supposed to win at WrestleMania 30, but Vince McMahon changed the decision late in the day.
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Talking about the change in the result of the match, The Undertaker said:
"I got to the arena that day and I was going over. I mean, we had gone back and forth and when I showed up, I was going over. Through the course of the day, Vince would come to me and say that he's changed his mind. man, I was like, 'Okay, I don't think Brock needs it, but at the end of the day, it's your show, it's your call. If you're sure about it, then that's what we'll do." [H/T Fightful]
The Undertaker, unfortunately, does not remember the match at all, as he was concussed and had to be rushed to the hospital.