You were talking to Iida, Izuku(Midoriya/Deku), and Uraraka(Ochaco), when All Might appeared.

"I.AM.HERE. He said proudly, smiling.

"Hi, All Might!" Izuku replied to the giant man.

"Hello, Young Midoriya, Hello, Young Yagi(Ur last name)."

You replied saying "Hi, dad.", realising you accidentally exposed All Might.

"DAD?!" Iida, Izuku, and Uraraka said confusedly. "All Might's your dad?!"

"... Eh... well... it's complicated." All Might replied nervously.