Complex sentence: It is likely Gaheris and Gareth were the same character in origin, as their names in French sources, Guerrehes (Gaheris, usually) and Gaheriet (Gareth, usually), are easy to confuse and adventures ascribed to the brothers are often interchangeable.
Split into simpler sentences: It is likely Gaheris and Gareth were the same character in origin. Their names in French sources, Guerrehes (Gaheris, usually) and Gaheriet (Gareth, usually), are easy to confuse and adventures ascribed to the brothers are often interchangeable.