It was pretty simple actually how it happened. We wrote and recorded it, and figured the ending would either just be instrumental with no solo, or that we'd fade it out perhaps. As part of the arrangement with Dan doing the mixing and stuff, we told him basically that if he had any ideas/suggestions for stuff that we'd be open to them. Apparently he really liked that song (he said it reminded him of an EoS feel) and had an idea for it, and he sent us the song back with his solo added. When we heard it of course right away we could tell that it was perfect for the song, and there you have it.
Now I get the fun task of playing it live, I really enjoy it, it's a good solo as you said. Another nice thing is that it kinda opened the door in my mind for putting more solos in our music. In the past I was never really into having longer more expressive solos in our music....I just never really thought it was necessary. After I heard how well Dan's solo worked in "Dark World Burden", I became more open to the idea. And now on this new cd, there's at least three songs where I perform full guitar solos. I'm nowhere near the player that Dan is, of course, but hopefully people will like the solos okay enough.