Dear Anton,
Working at a legislature has its perks and one of them is getting to know some consuls general!
I'm also a supporter of King Simeon, as is my monarchist league.
Yes, a number of Kyivan Metropolitans were Bulgarians and certainly Slavonic has also been called "Old Bulgarian."
King Svyatoslav, son of St Olha the Great of Kyiv, spent more time in Bulgaria than in Ukraine, as Bulgaria was such a great trading and cultural centre.
There is also, I believe, a Ukrainian scholar who spent his life working in Bulgaria and who has a monument to him in Sofia somewhere.
You wouldn't know more about him, would you?
Alex