The ending of Omen III: The Final Conflict wasn't the second coming at all.
Because Damien wasn't the antichrist Jesus was meant to stop. Think about it, if it was the second coming, there wouldn't be a fourth movie because we'd all be in Heaven. Damien fit the bill as the Antichrist we know from the bible, but he wasn't the final opponent Jesus is meant to fight. He was simply a placeholder for the kid in this movie.
