So I was trying to get the achievement about slaying a legendary dragon.

I was somewhere in skyrim on a mountain and met Paarthurnax (I did not know at that time you could not defeat him) for a second time. I just finished dragonborn btw.
I thought it was a legendary dragon. So I went up to him and chose another force upgrade shout (can't remember what I chose) - it's not a shout he learns you but a sort of enhancement of a shout.

Next thing I know I fast travelled with Serana (been my follower for a long time) and can't remember where, but right after I got that 'shout enhancement' I saw Shadowmere again and could ride him. I did get the same quest where I had to meet up with Delphine to do sth.

So meeting up with Paarthurnax relaunches the quest where you have to meet up with Delphine and gets you shadowmere.

My shadowmere died long ago, when I made a big ass jump into oblivion...

Not sure if this is dragonborn related.

Please delete.

Just found my answer. Apparently he resurrects at the place he died 10 days later. So I got lucky and fast travelled close to where he died.

I still got it!

Hmmm, very odd. I'll have to try that. My Shadowmere died a long time ago and contrary to what I have read he has never respawned again. I have since purchased a horse so I wonder if because I have anew horse (like having a follower) that Shadowmere won't ever respawn unless I get rid of it?

EDIT: Just saw your new post. I have heard of this before but I have no idea where he died. Seems odd you have to go to where he died AND THEN he will start following you again.

I'll try and find out what meeting up with Paarthurnax for the second time does. I did get that quest for the second time though. Could have been just lucky and travelled to the place he died.

Also, could switching to werewolf do something about it. I was a vampire lord for a long time, then switched to werewolf and I'm not sure, but I had to be in whiterun and a companion started talking to me. Isn't shadowmere related to the companions? - it's not - Dark brotherhood related

Hmm, makes me wonder if I did another Dark Brotherhood quest if it might help Shadwomere respawn? Doubt it, but might try.

I once lost Shadowmere and assumed that he must have died. I didn't always ride him and just left him wherever. Months later I found him standing outside Southwatch tower. To this day I still don't know whether he died and respawned or I just forgot where I left him!

Interesting. It's not possible to leave him somewhere, he will just show up at locations you fast travel to so it is quite possible he died at the location you found him. Or just some other dumb glitch of course.

no that happen to me on ps3.shadowmere die in spring 2012 and then we got that patch in august( dont remember patch number) after got that patch shadowmere return.

Shadowmere was slaughtered by a dragon at the doorstep of Lakeview Manor easily three months ago without returning... After DB was installed, Shadowmere was resurrected at that very spot at Lakeview for me as well.