It looks like a deformed yoke or maybe a floating piece of hen flesh that separated from the inside of the hens reproductive track and then got enclosed in the shell with a yoke and white. It is more or less normal, at least in so far as it isn't abnormal.
I have seen double yoked eggs that had one complete egg, yoke, white, shell and all, enclosed inside a second more or less complete egg including a separate yoke white and a second exterior shell. I saw one like that less than two weeks ago. It was a hatching egg farm reject but it still was a fine eating egg.