This is how The Tragedy of Galvatron goes in My Little Pony: Megatronus' Revenge.
[We see Megatronus Prime with Twilight in his lair]
Megatronus Prime: Did you ever hear the tragedy of Galvatron?
Twilight Sparkle: No.
Megatronus Prime: I thought not. It's not a story the other Princesses would tell you. It's a Cybertronian legend. Galvatron was a Decepticon leader, so powerful and so wise he could use the Energon to influence the midichlorians to create life. He had such a knowledge of the dark side that he could even keep the ones he cared about from dying.
Twilight Sparkle: He could actually...save anyone from death?
Megatronus Prime: The dark side is a pathway to many abilities some consider to be unnatural.
Twilight Sparkle: What happened to him?
Megatronus Prime: He became so powerful... the only thing he was afraid of was losing his power, which eventually, of course, he did. Unfortunately, he taught his apprentice everything he knew, then his apprentice killed him in his sleep. It's ironic he could save others from death, but not himself.
[Megatronus shows Twilight her future]
Twilight Sparkle: No! I will do such terrible things.
Megatronus Prime: Yes. But it doesn't have to be that way. The choice is still yours to make.
Twilight Sparkle: How?
Megatronus Prime: The future by its nature can be changed. Join me, and together we will destroy this Lord Tirek you see in your visions. Then we shall end war, corruption, and suffering throughout the galaxy.
Twilight Sparkle: Will we bring peace?
Megatronus Prime: Of course.
[Twilight's eyes turn red]
Twilight Sparkle: I can't make contact with anypony. I don't think anyone will hear my signal.
Megatronus Prime: My creator still has hold over this realm, but I will be able to draw any ship here soon.
Twilight Sparkle: If I know my old mentor, she, too, will try to stop us. Together with your creator, they would be a formidable opponent.
Megatronus Prime: I can turn the tide in our favor. Stay here.
[Megatronus transforms into his tank form and drives away from Twilight. Primus arrives]
Primus: What did he show you?
Twilight Sparkle: I've seen what I become, and I cannot let that happen.
Primus: And for this, you join him? Your destiny can change just as quickly as the love in one's heart can fade. Nothing is set in stone.
Twilight Sparkle: But I will cause so much pain.
Primus: If there is to be balance, what you have seen must be forgotten.
[Primus touches Twilight's horn, erasing what Megatronus showed her and returning her eyes to normal]
Twilight Sparkle: Where am I?
Primus: I have brought you back to Canterlot.
Twilight Sparkle: What happened?
Primus: Megatronus broke the laws of time and showed you what you should never have seen.
Twilight Sparkle: I don't remember.
Primus: I have erased that time. We shall never know.
Twilight Sparkle: What about Ryan? Where is he going to?