A new post on Marvel's Twitter account references a "Fallen Friend," saying that we'll find out all about who this character is at the end of next month.
The comic one-shot is set to come out in July, but from this "Fallen Friend" title, we can already guess who this might be about. It's likely this is a reference to the Fallen Son comic that followed up the death of Steve Rogers in Marvel comics in 2007.
<social>https://twitter.com/Marvel/status/1642981960317321218</social>
It's possible then that someone else from the Captain America comics could be up for the chop, though who that will be remains to be seen. Keep an eye on Marvel on the 31st of May for a full reveal of who this "Fallen Friend" might be.