He is implying XQ showed up just in time for the marriage as well - that was when he the third prince was implicated in the poison plot and would have had no way to compete for marriage (of course he later f-ed up his own chance by not showing up).
@ChristineH: I translated the OTP scenes from ep 13-19 (the ones not yet out or subbed on viki) here: https://mydramalist.com/28037-emperor-phoenix?r=notif&_nid=52375305#comment-5052103 Enjoy!