Yes! I read an article about that. Some lady was married and he fertilized an egg she had dropped and then she cheated on real soon after and happened to have dropped a second egg (thats pretty rare though) They had to do a DNA test because I guess the mom admitted to her husband so he wanted to see if the twins were his and only one was.
I think the father adopted the second twin that was his and her husband adopted the one that was his.
Yes very possible and quite a common occurrence