[He stayed quiet after Obito's questions, debating just how much he should share. Not that he didn't trust his student (and really, it didn't matter what was learned here), but it was habit to keep some of that information secret.]

...The Kyuubi was summoned into the village the night Naruto was born, and I used the Shiki Fūjin to seal away half of it. The rest was sealed into Naruto, making him a host.