Complex sentence: Cuthwine, then twenty-seven, was a commander in the fateful battle; but upon defeat, as the rightful heir to the throne, he fled the place and went into exile to the east with his young family (see below).
Split into simpler sentences: Cuthwine, then twenty-seven, was a commander in the fateful battle; but upon defeat, as the rightful heir to the throne, he fled the place along with his family. Cuthwine escaped from this defeat also, and went into exile to the east with his young family (see below).