Complex sentence: Another version of the events which led to Boleslaw's demise was propagated by Master Wincenty Kadłubek, who, however, was writing nearly 100 years after Gallus Anonymus and a century and a half after the actual affair.
Split into simpler sentences: Another version of the events which led to Boleslaw's demise was propagated by Master Vincentius Kadlubek. However, Master Kadlubek was writing nearly 100 years after Gallus Anonymus and a century and a half after the actual affair.