Board Thread:Naruto Discussions/@comment-24120130-20140607191120/@comment-24938412-20140608040730

Yeah, why not both? Sasuke appears to have the same design in his left eye, and it is stated to be a Rinnegan. And, Hagoromo said Kaguya possessed a Sharingan, which must be her Third Eye. Putting two and two together (among a few other statements in the manga), and viola, a hybrid of sorts.