Someone who isn't Jewish owns something which is chametz. He is storing it at a family members house. They understand it to belong to him and therefore won't eat this thing. Meanwhile he has forgotten about this and went through a gerus. Sometime later after having completed their gerus and having celebrated one pesach he returns to this family members house and realizes his chametz item is still there.
Who did this item belong to during the first pesach he celebrated when he had forgotten about it and may he partake of it now?