Hi

If I have song of kings and steward of gondor attached to a hero and I need to discard the song of kings card as a result of a shadow effect, do I have to discard steward of gondor too since the hero would lost the leadership sphere?

Thanks

There are two important points to make here. The first is that, although Steward of Gondor is a Leadership attachment, there is no requirement to play it only on a Leadership hero. The Sphere of a card only determines the heroes you can use to pay for a card. You can play an attachment on a hero of any sphere unless the card explicitly says otherwise (even heroes belonging to other players). If Steward of Gondor could only be played on Leadership heroes, it would say "Attach to a Leadership hero".

Secondly, in this game, an attachment only checks whether it's legal to be played on a card at the moment the card is played. So, even if Steward of Gondor could only be attached to a Leadership hero, this would only be checked at the moment you play the card, so in the situation you describe, the Steward of Gondor would remain attached.