Headcanon #8:
September 1st, 2017: James Sirius Potter teased his brother, Albus Severus, during the whole day, right? Yes. The reason? James "thought" that Albus would go to Slytherin, this thought was more to tease him. When Al's sorting finally came, guess what? The hat did not yell 'Gryffindor'; instead, it yelled 'Slytherin'. James was surprised; they were brothers, but they were so different...
Everybody was laughing at Albus. Almost every single student on the Great Hall. "Look, seems like he's not a real Potter!", someone said. But here's the thing; James wasn't laughing. Albus' brother, his brother, the prankster, the one who always teased him, didn't laugh at him. He was actually... clapping his hands. And telling everyone who was laughing to shut up. All that moments, all those times that Albus got angry at him seemed wrong; his brother was standing up for him. The young Potter couldn't be more grateful. He looked at his older brother, who smiled and nodded. You didn't deserve that. You should be proud.