Relevant text of Mortal Strike:
R Commit: After your opponent's Ready Phase, until the beginning of your opponent's next turn, players may not add cards to their momentum during the Combat Phase.
Relevant text of Demuth's Sponsorship:
R Commit: After an attack you completely block resolves, reveal the top card of your deck. If it is an attack, play it as a Reversal (no control check necessary). Otherwise, add that card to your momentum.
My question is this: If my opponent has used Mortal Strike on my turn, and I then use Demuth's on his turn after blocking his attack, and a non-attack card is revealed, what happens to it? Does it stay on top of my deck, get discarded, or does something else happen?