Does his response trigger before or after the event card executes?

Cool question. This could be relevant for, e.g., the Daeron's Runes interaction: is the forced discard from cards #1/2, or #2/3?

I think the response triggers before event card execution. Otherwise you'd have the odd issue of executing the entire text of a card, then adding some more (Doomed 1) and saying, oh yeah, do this Doomed thing too.

Circumstantial evidence includes:

* the FAQ distinction between "when" and "after"

* the Dol Guldur Beastmaster erratum

* the fact that the encounter card Doomed keyword triggers before most regular text on the card

(Actually, I'm not so sure on that last point, although it does appear that way in Seastan's reveal guide. Anyone else have insight?)

I agree about resolving Steward of Orthanc ability before the event.