-( Story related, cannot be missed )-
First note: you can get this early if you go for the Early End trophy as well:
If you didn't get this then, you will get this later during your fight with him in Sokrevenno during Operation Snake Eater.
Second note: The fight against The End isn't like the previous fights against the COBRA Unit. It is a test of patience, stealth, or being riddled with holes. The End will poise himself among weeds, using a higher spot to take you down. He will hide in any of the three sections of Sokrevenno carefully picking you off. His sniper rifle will create a brief lens flare every now and then when you two can see one another. If you take your time to sneak through, you can easily navigate through the terrain to get behind him and get a few shots in. Sneaking up on him would be preferable for two reasons: the Moss camouflage obtained from holding him up is good for two trophies.
Third note: The End appears on thermal as well as the lens flare giving him away. If you also look into your Map in the Survival Menu, you will find several white circles; these are possible sniping positions that he will be hiding in. If you use your Thermal to find him, you can either sneak behind him (using the Directional Pad, not the joystick) to shoot him some or you can use the position to your advantage and just directly shoot him.
Fourth note: After you find him and surprise him, hold him up for a bit, or shoot him, he'll either retaliate (if you were too loud on sneaking up on him) and/or just drop a flash bomb before running to his next point. If you pay enough attention, you can actually follow behind him some and, once he starts breathing heavily and stops at a new point, you can sneak up on him and continue. Should you be too slow, wait a bit and his footprints will start to show up in Thermal, allowing you to hunt the hunter.
Fifth note: since you acquire his camouflage differently from the way the others were obtained, the reward for killing him by depleting his stamina is his sniper rifle, the Mosin-Nagant. Once he dies, you will find this in the far northwest of Sokrevenno North.
Should there be any concerns or misinformation, please let me know rather than rating the solution down.