Ladybug and Chat Noir had finally made it to his lair, and Hawkmoth felt a flare of excitement for the big reveal. Oh, he was sure they knew already, but the drama of it all! He clears his throat and tries to seem angry.
"Ladybug! Chat Noir! Get ready for defeat! You dare invade my own home? I'll destroy you and take your miraculous!"
"Not if we take you down first Hawkmoth!" Both Ladybug and Chat Noir are furious. Holing up in the Agreste mansion? The nerve!
"Mayura! Help me fight these children and take their miraculous!"
Both Nathalie and Gabriel cover their practiced moves as they carefully evade and block the superheroes' moves. Just as planned though, they're just barely caught and apprehended.
"Now to find out who you really are!" The superheroes wait for their transformations to be completely undone. Gabriel hears gasps. "Gabriel Agreste and Nathalie? But why?"
This was all part of the act right? There was no way they actually didn't know. It was so obvious! He coughs and says, "Well done children. You've completely and utterly caught me. What now?"
Ladybug and Chat Noir look at each other. "We take you to jail of course for your crimes, Hawkmoth." Weirdly though, they seemed uncertain.
"Come on, we can stop with the act now. You knew it was me all along. It was a friendly sort of rivalry, no? And no one really came to any real harm. Come on Adrien and Marinette, lighten up a little." Gabriel approaches the two and they freeze.
"How did you know?"
Gabriel blinks. "I could see everything in the city as Hawkmoth. How could anyone not know? Your appearances stayed almost completely the same when you transformed, and you did nothing to try to disguise your voice. And when both of you were regularly missing? Common sense, really. I even played it up and acted like I didn't know my own son was leaving the house all the time and had a crush on his classmate turned superhero partner. Real cute actually. You two should confess already."
Ladybug and Chat Noir blanche. This is not at all what they had expected from this confrontation and they proceed to detransform.
"Then what about your wife? You kept saying you wanted our miraculous so you could bring Emilie out of a coma!" Marinette says accusingly.
"Emilie?" Gabriel looks confused. "I only read about the wish thing in the miraculous book, and Emilie's fine. We're divorced. Completely mutual. She just agreed that I could use her name for this supervillain scheme. You really didn't know?"
Adrien shakes. "Then Mom's been fine this entire time?"
Gabriel exclaims, "Of course she is! Everyone's fine! This was all a huge act so I could help stressed people have a cathartic outlet for their emotions, and you would come and rescue them. I know the long term consequences of stress and burnout better than anyone, and I wouldn't wish it on anybody. And you'd be damage control if things did get out of hand. You could have contacted her and anyone else at any time. I just thought it was about time I put an end to this since I still have a fashion company to run. It's been fun, but I just don't have the time or energy anymore, you know?"
Marinette shakes her head. "But Mr. Agreste, no one knew this."
"But - " Gabriel thinks. "I've always made it manageable for you two. I made sure no one was ever in any real danger, you were able to lead successful double lives, and every akumatization pretty much ran on a script. You really didn't suspect a thing? I thought civilians might not, but you? I thought you were smarter than this!"
"But then, what about Mayura? You were probably manipulating Nathalie from the shadows!" Adrien shouts.
Nathalie shakes her head. "Absolutely not. I did all this out of my own free will to help Mr. Agreste with his villain roleplay. I never thought it'd go on for this long."
The four proceed to discuss all their misunderstandings and come to the realization that continuing this game of superhero and supervillain would no longer be constructive or an honest use of their time. While a little disappointed that it had to end, Gabriel Agreste joins an acting class with Nathalie to continue his newfound interest in acting as well as designing clothing, and he and the heroes still meet regularly to play superhero and supervillain with a tabletop roleplaying game to avoid the property damage but keep the fun of saving the city. Marinette and Adrien enjoy the new normalcy of everyday life and romance, and everyone is happy.