Forum:How does lord of D's effect work

My brother and I disagree on how lord of d's effect works here's the scenario

My field 4 dragons 1 lord of d

He plays Final Destiny, I think that it would kill only lord of d with his effect protecting my dragons for this card

He thinks that since it kills lord of d it would also kill my dragons

who's right?

also he has a trap card that says to discard monsters on the field until we each only have 1 monster on the field

I think that since lord of d protects the dragons from the effect that lord of d would count as the 1 card with my dragons being immune