This is how Starlight, Trixie, Thorax, and Discord discover Thunderwing and Thunderwing forms an alliance with the Changelings goes in Transformers Prime: Attack of the Changelings and Thunderwing.
[Starlight, Trixie, Thorax, and Discord see a purple meteor crash into the Everfree Forest]
Starlight Glimmer: What was that?
Trixie: It looked like a meteor.
Thorax: And a purple one too.
Discord: Let's check it out.
[They go to the Everfree Forest and run through it until they come across the Dark Energon meteor and inside is Thunderwing half-buried in the Dark Energon meteor with only his head, torso, and right arm sticking out]
Starlight Glimmer: Whoa!
Trixie: He's a big one.
Thorax: Well, I've never seen him before. Is he dead?
Discord: Just give him a nudge. [nudges Thunderwing's finger]
Starlight Glimmer: Be careful.
Thorax: It was just a tiny nudge.
Discord: I guess he is dead.
[Thunderwing's fingers start moving, which none of the four notice. Thunderwing raises his arm to smack Starlight away, but Thorax notices.]
Thorax: Starlight look out! [grabs Starlight with his magic and pulls her away from Thunderwing just as his hand is about to smack her away.]
Thunderwing: Death to the Elements of Harmony!
[Thunderwing raises his fist to smash Starlight, Trixie, Thorax, and Discord, but they move out of the way.]
Starlight Glimmer: What's he talking about?
Trixie: He said "Death to the Elements" so he must have the desire to destroy them.
Thorax: That's what I was about to say.
Discord: This is not good.
Thunderwing: I don't have a desire to destroy the Elements of Harmony. It is my mission to destroy the Elements of Harmony by my master, Unicron the Chaos Bringer!
Starlight Glimmer: What?!
Trixie: Oh, no!
Discord: Not good, not good, not good!
Thunderwing: I like not good.
Starlight Glimmer: Run!
Trixie: Come on!
Discord: We must keep him from the elements.
Thunderwing: Nothing will keep Thunderwing from the Elements of Harmony!
Starlight Glimmer: Hurry!
Trixie: Come on!
Thorax: Let's go!
Thunderwing: Yes. Run all you want.
[Thunderwing starts attacking the group until the Changelings arrive]
Queen Chrysalis: Changelings attack.
Starlight Glimmer: Let's go while he's busy fighting the Changelings.
Trixie: I agree.
Thorax: We must warn Twilight.
[At the Changeling Kingdom]
Changeling: He's definitely incomplete. Once we pull him out of the meteorite, I'm afraid he'll look like a puzzle with pieces missing.
Queen Chrysalis: Your ability to state the obvious staggers the imagination.
Changeling: My apologies, Queen Chrysalis. Some of the missing components may have been embedded in fragments of the meteor that split off and fell in other locations.
Queen Chrysalis: I see. Wake him up.
Changeling: Yes, Queen Chrysalis.
[Thunderwing wakes up and looks around at his new surroundings and looks down and sees his legs are stuck to green goo.]
Thunderwing: I am Thunderwing. Release me immediatly!
Queen Chrysalis: I am Queen Chrysalis, leader of the Changelings.
Thunderwing: Your name means nothing to me. I exist only to destroy the Elements of Harmony! Release me so that I may find their wielders and complete my mission!
Queen Chrysalis: Seems to me that you are in no position to make demands, Thunderwing. Even if I did released you, your body has taken on too much damage to function. However, if you swear your loyalty to the Changelings and to me, then I promise you that I will have you repaired and provide you the opportunity to destroy the Elements of Harmony.
Thunderwing: HA! You, repair me? You cannot even comprehend how long have I existed. The technology of my construction is beyond your grasp.
Queen Chrysalis: On the contrary, my knowledge of Cybertronian Physiology is unparalleled.
Thunderwing: So be it. But understand this, Queen Chrysalis. Once the Elements are gone, my loyalty will return to my one true master, Unicron the Destroyer!
Queen Chrysalis: [to herself] We shall see. [to Changelings] Find all the locations where the fragments of the meteor fell to Equestria.