Perhaps, this is the one of the few times that Alexander and Tristan are on the same page.
It has already been an hour since the party at Ruben's restaurant started, and everyone who was invited has already arrived - all except for that one person who should have been there the most. Lillian still hasn't shown up yet.
She's never the type to run late when it comes to this kind of gatherings. Knowing her, she also would've already gone there an hour earlier to help with the preparations.
No matter what the reason they could possibly come up with, not showing up for this long is already a bit of a stretch. Nighttime is about to fall, which will then make the streets dangerous for a lone girl to tread.
With these in mind, the two of them finally decided to spring into action and look for Lillian - in such an impeccable timing at that. It just happened that they thought of the same thing at the same time, causing them to act in complete sync.