Complex sentence: Thirlwall fought alongside Richard during his final charge against Henry VII, which was considered as the "swan song of medieval chivalry" as he was his standard bearer, where he was slain after the intervention of Sir William Stanley and his force.
Split into simpler sentences: Thirlwall fought alongside Richard during his final charge against Henry VII-which was considered as the "swan song of medieval chivalry"-as he was his standard bearer. He was slain after the intervention of Sir William Stanley and his force.