Whether it's the earliest depends on where you draw the borders for Eastern Europe. Specifically, the border between Europe and Asia. If you're willing to go as far East as the the north Caucasus, there is a 4th century Alan blade from Kislovodsk, and other early crucible steel weapons from the area.
There are also the crucible steel Ulfberht swords, some of which were found in what is without doubt Eastern Europe. While not as old as the Alan sword noted above, they are older than the 1238 dating of this sabre.
I also have vague memories of early crucible steel swords from Ukraine.
(For the Alan sword, see Ann Feuerbach's thesis,
http://discovery.ucl.ac.uk/1317704/ )