 Complete the following phrase:  Ivans role in the final years of Tsar Michael Shishmans reign and the rule of Ivan Stephen is uncertain, as he is not mentioned in the sources pertaining to that period. His high-ranking position nevertheless leads Pavlov to conjecture that Ivan took part in the Battle of Velbazhd of 28 July 1330, a Serbian victory over Bulgaria that paved the way to the Serbian domice of the Balkans in the mid-14th century. Michael Shishman was killed in the battle and succeeded by his son Ivan Stephen 13301331. Pavlov believes that Ivan the Russian was among the Bulgarian nobles that ousted the weak Ivan Stephen in 1331 and placed Ivan Alexander 13311371 on the throne. It is also probable that Ivan the Russian took part in the Bulgarian victory over Byzantium 