Complex sentence: Freeman also suggests that an earlier version Senlac was "Sand Lake" in Old English whereas the Norman conquerors called it, in French, "Sanguelac" (and variants) which he regarded as a pun because Sanguelac means "blood lake" in English.
Split into simpler sentences: Freeman also suggests that Senlac had been known as "Sand Lake" in Old English and that the Norman conquerors called it, in French, "Sanguelac". Freeman regarded this as a pun because Sanguelac means "blood lake" in English.