The End, dying of Old Age.

[Moriatti]

You do recall. Beyond this there's sniping him WELL BEFORE the mission.
You can also anger him by killing his bird, though unfortunately, capturing and eating it infront of him does not appear to trigger this effect. (I tried.)
In addition, if you capture and release his bird, it will fly around him irritated, forcing him to shoot it. (Remember he uses tranq rounds.)

The End is also unique in that killing him by stamina forces him to drop his weapon, NOT his camo as per the other bosses. You get that by holding him up, something not possible with any of the other bosses.