User blog comment:IamJakuhoRaikoben/Chapter 457: Naked Battle, Review./@comment-4829046-20151019173906/@comment-26416024-20151020004356

Until more info is given, the obvious answer as to how Natsu ended up in Igneel's care was that he was at least somewhat responsible for sealing Natsu's powers and memories in the Book of E.N.D. Don't forget that Natsu was the guild master of Tartaros.