Modern Bulgarians are genetically closest to their neighbours (duh), so Romanians, Serbs, Macedonians, Northern Greeks and, yes, probably European Turks (and, yes, European Turks and the coastal ones in Asia Minor are genetically descended mostly from Greeks/Hellenized locals and Slavs). No big deal here – the biggest genetic shifts in our region are in prehistoric times, while in historic ones it’s mostly the culture that changes.
Btw, @Sviatogor, I recently visited Shipka and the Russian church in the village. Perhaps you should visit it one day as well, if you come to this area – it’s a very majestic (and expensive) church and there were a lot of names of members of the Russian army who’d fallen there. Sadly, I didn’t take any photos of them, as they’re too many and I felt uncomfortable taking pictures inside the church…