I case anyone wants to read it this is the story the artist has on the deviantart page
Lord Tirek, once the most feared creature in all Equestria, had been imprisoned once again in Tartarus. It was a horrid place, where people went mad in the solitude and darkness.
The only reason he was no longer there was due to one little filly.
It had been years later when a filly known as Flurry Heart had broken into Tartarus. At first, Tirek had been irritated, but soon realized he preferred any sort of company, even that of a little weak pony, rather than none. It had taken a long time, but soon she revealed herself to be an alicorn of all things. Tirek was surprised, yet it had worked out for him.
The filly had begged Princess Celestia to allow him a parole of sorts, to be freed of Tartarus and teach him friendship. Tirek, of course, was not excited but took any chance he could to not stay in the pits of Tartarus forever.
Now the filly became something a nuisance, but he only ever said that to try and relief himself of the embarrassment it would endow upon him if he ever admitted to enjoying the little princess’s company.
In his room in the castle, which he had been given only to be kept an eye on, he had been reading in order to satiate his boredom. He was not allowed very often in the public. For one, he could turn evil once more and begin draining ponies of their magic, and two, he was still a very threatening figure, even if he was not at full power.
He was fully distracted with a book when he heard tiny hoof steps approaching his door. He didn’t even bother to see who it was as the door was opened.
“Tirry!” The filly nearly shouted. Flurry Heart was no longer exactly a filly, a teenage mare to be exact. Still, she was young and was far too comfortable around the centaur, even giving him a nickname. Flurry hopped up on a pile of books, resting her front hooves on his side. Tirek turned to face her, raising an eyebrow.
“Does your mother know you are here?” He asked, trying his best to seem annoyed with her. Flurry wasn’t fazed, having long since able to see past his grumpy exterior.
“Nah. I snuck away while she and Aunty Twiley and Aunty Celestia were talking. How are you?” She gave him a blinding smile, which he rolled his eyes at.
“Reading books. I haven’t had much of an opportunity to go outside. Too many little ponies. Your Princess said it was too dangerous to allow me outside during the day.” He set his book down, frowning.
Flurry Heart frowned as well, which was not a good look for her. She paused, thinking before turning back to the centaur. “Nonsense! I’m a princess too, which means I can allow you to go outside!”
Lord Tirek stared at her, “You do realize that you are only a Princess in the Crystal Empire, correct? You do not have the power to allow–”
“C’moooon. You wanna go outside, and I wanna let you! I’ll take the blame entirely, promise.” She crossed her heart with her hoof, giving him a sweet smile. Tirek blinked, once again taken off guard by the sweetness and naivety of the filly he had begrudgingly befriended. Sighing, he began to stand just as the filly flapped her oversized wings to land on top of his back.
“Fine. I will do this…. if only to get you in trouble.”