How to react when finding things from an ex in significant others home?

My fiancees grandmother just died. We recently got engaged and haven't moved in together yet because we're renovating our apartment. He's out handling funeral matters and I'm at his place and thought I'd bake his favorite dessert.

I was looking for batteries for the food scale and I found a card from his ex in a drawer. I've told him before to get rid of whatever things he has from his ex. Pictures, presents, everything.

Of course I'm furious. Could be an honest mistake but he's promised me that he's looked through everything and cleared things out. How do I react. Obviously I can't bring it up now when his grandmother just died. Do I leave at least? Do I stay and be here for him and act normal until the grief period is over?

How to react when finding things from an ex in significant others home?
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