Macro cosmos+horus Lev4/6

I want to activate horus Lev4 to special summon Lev6, and Macro cosmos was on the field. My opponent told me I can't because I must send it to the grave not to RFG.

DRAGON LV4
[Dragon/Effect]
During the End Phase of a turn that this card destroyed a monster by battle, by sending this card to the Graveyard, Special Summon 1 "Horus the Black Flame Dragon LV6" from your hand or Deck.

Who's right? And why please?

your opponent is right because Horus Lv4 effect's says that you have to send it to the grave and since Macro Cosmos is on the field so your monster won't be sent to grave but will be removed from play instead (which means he didn't hit the grave at all)
therefore you can't level up your Horus
I hope this helped you

More specifically, sending Horus LV4 to the grave is a COST to special summon Horus LV6. This is a cost that cannot be paid while Macro Cosmos is on the field and therefore the effect cannot be activated. Note that as long as sending a card to the grave is a part of a cards EFFECT and not a COST you will be able to activate that card.

Ask Neokofjung said. And it is obvious on the card's description.
Question Answered.
Topic Closed.