Justin was there! He talked with everyone who was there and tried not to be uncomfortable with both Charity and Polaris being with him in a social situation. During school it's different, but this is a party so cmon cut the kid some slack. He was ready for a party so he definitely had plenty of fun.
By the time he left, he was tipsy like the rest of them, so he might've asked to crash with someone in the village as opposed to wandering back to the castle in the middle of the night while slightly intoxicated. But he was very happy and very much in a celebratory mood.
Hat and noisemaker were used. Hat was worn all night long. It was an awesome neon colored one.