Pensieve

After casting the Patronus Charm, Remus Lupin turned to look at his companions. He had dreamt of hearing James's voice - and there he was, right in front of him, but much younger. Remus blinked, and stared, not into James's warm hazel eyes, but into Lily's startlingly green ones. He looked away in the pretense of looking for chocolate, before Harry or his friends could see the tears in his eyes.

Harry fell unconscious. Remus's heart broke, to see Harry on the ground, to realise how badly the dementors affected him because of the horrors of his past, to know that Harry did not recognise him, even though it were only his cuddles that used to calm Remus's rough days 12 years ago.

Remus's heart broke to see all that this little boy could have had, but didn't.