Complex sentence: The Doctor speculated that Dodo might be Anne's descendant, and as some have pointed out, that would mean Anne lived to have an illegitimate offspring (unless she married a man of the same name).
Split into simpler sentences: The Doctor speculated that Dodo might be Anne's descendant. As some have pointed out, that would mean Anne lived to have an illegitimate offspring (unless she married a man of the same name).