We were originally just going to play a standard game and I was just going to use the "Soul Glaive", but he surprised me with An'ggrath and we both thought it would be cool to have the Bone Shard of Solor in use (considering he ended up being mono khorne).
The Grand Master entry states he can take items(plural) from the Relics of Titan list, and the same argument has been had many times in the Space Marine codex. I can't say one way or another the official ruling, but both my opponent and I were cool with it.
Hope you enjoyed the report!