How To Unlock:
Stealthily enter the manor in 'Better late than never' mission.
“Better late than never” is the third and last mission of the Unfinished Business campaign. You have to enter the manor without being spotted by the guards, so sneak past them or take them out stealthily. Some people (including me) have difficulties unlocking this trophy, and again, the only solution found so far is to delete your game saves and try again.
NOTE: When I got this trophy, I did a few things differently: 01. Don't rush. Everytime you stand or run, you may get noticed. 02. In the second camp, I did not go across to the checkpoint. I followed the video to the building in the centre of the base, and then turned right towards the bridge. Crawling forward, I hid in a bush and took out the two guards in the two towers, as well as the other two pacing guards. 03. When you reach the end of the first video, you come to the area with the far off sniper. I approached the checkpoint just before this while crawling on the ground. Stay close to a bush, and he should not be able to spot you. This is where the main glitch is supposed to occur.