I read this fic ages ago on AO3. I'm fairly certain it was before CACW/Tom Holland spider-man entered the scene, so pre-2016ish
What I remember was that Peter (Andrew Garfield version, I'm pretty sure) was in high school when the Chitauri invasion happened in The Avengers, and the teacher turned on the TV so they could watch the news. Peter is Tony's bio son, and Tony called him as he's about to take the nuke to space. (I'm pretty sure he also told Peter to look away from the screen and not watch??)
But basically, Peter just decides to nope out and makes his way to the heart of the battle to get to his dad. He also brings Gwen along with him because her dad is also out there as a cop. And then Peter finds Tony and it's really emotional.
This could be part of a longer story?? Or a series?? But Tony raised Peter from a very young age and kept him a secret until now. I've been searching for this fic for months and greatly appreciate anyone who can help me find it!! 🙏🏼
edit: I found it!! The fic is
Reveal by CreativityFlow