The Picture of Dorian Gray/WMG

Oscar Wilde was a Janeite.
The Ho Yay-packed The Picture of Dorian Gray is basically a Gender Flipped version of the Les Yay-packed Emma. Emma even paints Harriet's portrait!

Dorian is a wizard and doesn't know it.
When he murdered Sybil Vane (albeit indirectly), he unconsciously turned his portrait (an object he'd invested a good deal of his soul in) into a Horcrux.
 * Oh, no, he definitely lost at least part of his soul before Sybil Vane died, hence his nastiness toward her that drove her to suicide

Lord Henry is a Slaaneshi Cultist.
Think about it, he corrupts an open mind to become a hedonistic monstrosity, and there was clearly someone listening when Dorian made his wish that the portrait would age instead of himself. I'm willing to bet there was a Mark of Slaanesh hidden on that portrait somewhere.

Dorian's Deal with the Devil was acknowledged and accepted, but it didn't actually take effect until it got to the point where he would have started showing visible signs of age
When Dorian impulsively says that he'd sell his soul for his painted figure to age and for himself to have eternal youth and beauty, it's not like he becomes The Soulless immediately afterward. For a while afterward, he is going to see the Shakespeare plays that Sybil Vane performs in and falls in love with her to the point where he has promised to marry her and, from what he says of her, she has become his Morality Pet. During her last performance that he sees, though, they have both found true love for each other. So obviously, at that point, he had still not lost his soul. Undoubtedly, since he was falling more deeply in love with Sybil, he was smiling at least almost every time he was around her. He was probably smiling so much that, had he not made his Deal with the Devil, it would have made at least a slight wrinkle or wrinkles somewhere on Dorian's face that would not be immediately noticeable, but visible to anyone who really took the trouble to notice. Since he made that Deal with the Devil, though, he lost his soul at the very point where he would have started wrinkling and changing in appearance from age. In exchange, he didn't start wrinkling, but the portrait did, and the only reason he didn't notice was because he was so callous toward Sybil Vane that his cruelty was reflected in a smirk that was more noticeable than a slight wrinkle.