Everyone was surrounding the fight, not going past police barriers of course, and watching as the depression based akuma fought with the heroes of Paris.
While the duo was planning, the akuma hit Chat Noir in the back, shocking everyone when he didn't notice. When the akuma hit someone, they usually started bawling right on the spot, or had a panic attack, or couldn't talk, or snapped at everyone, or was unusually overly happy.
He did notice, when Ladybug jumped over him and started raging on the akuma. He then noticed that everyone was gaping at him. He waved awkwardly, and jumped into the fight, but he was not needed as Ladybug's rage about her Chaton was apparently enough to stop the akuma.
Everything was quiet, when Ladybug let her transformation time out and hugged Chat Noir tightly ranting about how his depression shouldn't even exist, why would I want it amplified?
"Are you sure you weren't the one to get hit with The Depressers hit? Because you just transformed in front of all of Paris, princess." Chat chuckled, hugging her back. An "I don't care." was heard.
Ladybug then pulled back from Chat Noir to look at the crowd, who then was let known that Ladybug was a girl about 15 years old, with casual clothes. A certain Ladyblogger gasped and jumped over the police barricades, running up to her best friend.
Alya Cesaire cried that day. Especially when Chat's transformation dropped as soon as she finished hugging her best friend to death. She then started sobbing crying when she saw Adrien-motherfucking-Agreste was Chat Noir.
She then yelled at the two in front of the crowd for how stupid and dangerous it is and "What if you died while fighting an akuma and went missing and no-one would know because you dinguses only told each other who you were? What would we do then?