"Thorax? It's Twilight!" came a voice from the door, accompanied by a quick series of knocks. "I'd like to speak to you about your horns!"
Thorax froze, his eyes darting towards the discarded neon-green suit that lay on his bed. Turning towards the mirror on his dresser, he remembered one little, itsy-bitsy, fatal flaw in him being the supposed "King of Changelings", or whatever they were called now.
He was actually a moose with limited shapeshifting abilities aided by curiously high-tech bodysuits from another galaxy. The original Thorax was accidentally smited by his landing shuttle, and so naturally, Moosy McMooseface replaced the little bugger.
But after experiencing his... coronation of sorts, it had only become harder for him to hide his true form.
Obviously, it was already too late for that, however, because...
"Thorax! Come on, your speech to Ponyville is almo--wut."
Here stood Thorax, King of all Changelings, struggling to fit himself into costume, and from Twilight's perspective, appeared to be molting his exoskeleton.
"Look, I can explain." Thorax nervously chuckled, holding up a drooping hoof of the costume.
"No, no." Twilight replied as she closed the door, "I'll just tell them that you're um... busy."
Later that night, Spike swore he heard Twilight screaming about changeling-moose crossbreeds.