Arrived at the Pride Lands/Finding Simba/Fight against Scar

This is how Thunderwing takes control of Twilight and Twilight finds Dark Energon shard goes in Thunderwing's Revenge.

Princess Celestia: Twilight what have you been doing? [sees she has Dark Energon] Dark Energon?

[Twilight knocks out Celestia with a blast of magic]

Optimus Prime: The only one who knew of the shard...was Thunderwing.

Starlight Glimmer: Twilight has Thunderwing's memories?

Optimus Prime: Worst. Thunderwing is occupying Twilight's mind.