Thinking about it, Zion was still young. Despite being exceptionally intelligent, he was still a person with flaws of his own. So, seeing how confused Zion had looked after Suga gave birth was honestly a little endearing, while also making William feel somewhat bittersweet.
It was endearing because William had never imagined Zion could be capable of feeling that way toward another human being. The only person who could make Zion experience so many emotions all at once was Suga.
And it was bittersweet because that confused, pale expression on Zion's face was familiar to William. It was exactly the same expression he had seen on Andrew's face when Andrew immediately voiced his concerns while accompanying William through the C-section when he gave birth to Kimberly.
