User blog comment:HollowIchigo58/High School DxD Season 4 Announced/@comment-2143738-20161026021545/@comment-9595671-20161026032125

Yeah, he'll probably appear around the final last episode for a bit, likely near the last scene but not the exact last scene since so far each anime's final scene has ended on a happy note...

Unless they wanted to guarantee a sequel by giving us a sequel hook scene