Legolas first encountered death in Moria, when he saw Gandalf fall. He did not understand, at first - were not the Istari immortal? How could Gandalf really be gone? His insistence that it was not so was borne out, later, when the wizard returned.
His second experience came near Rauros falls, when he watched Boromir die. This time he was merely curious. Boromir was mortal, and mortals died. That was the way of it. But Legolas had never seen it happen before.
The third time, it was one of his own kind. He did not see Haldir of Lorien fall, but Aragorn assured him the elf had fought to the end.
That grief, more than the two others combined, nearly killed Legolas.
Harry was sorting through the photos he had inherited when he found it.
Sirius was gone, and Remus had retreated into the mountains, to a place of gathering for werewolves. He had left Harry all Sirius' belongings, and everything else he would not need.
Harry didn't think he could have found this picture, or he would have taken it with him. The things it showed shouldn't be seen by just anybody. Oh, it was perfectly innocent to a casual viewer: there was James and Lily, and Sirius, Remus and Peter.
But the look in Sirius' eyes as he gazed at James made it intensely private.