Theory about Ras's master

Maybe it is one or both of the time twins. We have not seen them since the end of season 7 (i think. I dont remember). The master want to control the source dragons and reverse the merge. It could be that the time twins need the energy from the source dragons to get their powers strong enough to reverse the merge. The reason the master is refered to as only one might be that one of them lost their brother in the merge and therefor wants to reverse the merge to get them back. How this relates...