Shadowmere has magically vanished, I thought it might have been like in Oblivion where he respawns where you first find him, but he's not there at the sanctuary, and he's not dead, I've searched around in-game and on the internet and most people say it's a glitch, but I was just wondering if this can or will be fixed.
Any ideas or help would be greatly appreciated.

Tried all the stables outside the cities?

He can die from fall damage, so he might've ran off after some mildly aggresive rabbit and fallen to his squishy death.

There's a console command for PC users that lets you teleport to him, or him to you I think.

damn orcs probally ate em tisk tisk :shakehead:

hes probably off killing dragons i rode him once and left there i come out off whiterun and look over to the tower hes there fighting 1 and killed it wtf am i here 4 then

Shadowmere is the OG Dragonborn.

No idea, the same thing happened to me. I really really hope they fix this problem because I want my dang horse back! Shadowmere is a boss.

When I changed horse, the previous one disappeared. I found darling Frost just outside one barrow, though. He can stay there for all I care because I now ride Shadowmere.

Have you changed your horse? Or sometimes, I think, the horse doesn't follow you on fast travel, especially if you use it when you're far away from your horse. Always fast travel while riding or near your horse.

same thing happened to me, he's gone off somewhere. He did annoy me how he followed you EVERYWHERE though -.- i wanted a 'stay here' or '[censored] off home now' option sometimes.