Tempest reveals Shadow Mane was her student

This is how Tempest reveals Shadow Mane was her student goes in Ghost Story.

[The ponies, Autobots, and Tempest sit round a camp fire]

Tempest Shadow: I have something to tell you all. Something I should've told you a long time.

Applejack: Really?

Bulkhead: Is this about how the Storm King hired you to be his lieutenant? Or is it about Shadow Mane?

Tempest Shadow: Shadow Mane may have been my first student, but he was also my greatest regret.

[A flashback to when Tempest worked for the Storm King]

[She places a spare down]

Tempest Shadow: (voice over) Before he was a successor of the Pony of Shadows, it wasn't I who found him.

[A young Shadow Mane comes over]

Tempest Shadow: (voice over) But he who found me. My partner Grubber had just gone off to find more Storm King troopers, which gave me time to more teaching. Shadow Mane was the perfect student.