I noticed it on a rewatch! We must've missed him the first time because he wasn't in the lineup with the other siblings, and I think it caught me off-guard because they made sure that Arya squeezed between Sansa and Bran. I figured there was some sort of a Vontrap kids age lineup deal that was polite when saying whats up to the king. I was so happy to see him there when I rewatched, though, and his reaction to Robert absolutely was perfect.