Sam uses Dean's phone and finds a whole photo album titled 'Cas' which contains photos of Cas. Most of them were taken without Cas knowing. He scrolls through many pictures and comes across a video. It's of them sitting on Dean's bed with Dean saying "who are you?" and Cas replying "I'm Castiel Winchester". Sam smiles at this. He smiles even harder when he sees that Dean's home screen is a picture of the three of them, Cas in the middle, all smiling; that's his favourite photo.
This is beautiful, anon. Thank you.