It's here that Adrien learns Marinette's whole deal; that she's been in love with him since "the umbrella" and that she wasn't with Luka.
It's only here after he realizes that there were significantly less people in their complicated relationship that he bought the three of them a mansion meant for a dozen people, telling this to Marinette after he had already gotten it.
Like Father, Like Son: Marinette lampshades that Adrien buying a house for everyone without asking them first is something Gabriel would have done, though she doesn't harp on him over it.
Rewatch Bonus: In-Universe. Both Adrien and Marinette acknowledge that they really should have realized their secret-identities before, considering the number of times they leave, only for their superhero identities to show up moments later.
Secret-Keeper: Marinette's doctor agrees to keep Ladybug and Cat Noir's secret identities a secret.
