I remember seeing the Siliconera article which first leaked that the remake would be announced at Sony's E3 conference later that day. It was different from previous leaks. Siliconera did not prepend the article with "RUMOR". They put their whole reputation on the line.
I believed it. I had to work that night and knew I'd be closing up the shop by the time Sony's conference rolled around. I planned to listen in with my headphones. Cleaning the dishes, I heard the speaker claim the next announcement was special or something. Pulled out my phone. Wasn't sure what I was looking at at first, but when the first few notes of Beyond the Wasteland from AC played, I knew. Jumped up and down a few times, slammed the countertops around me, probably made a few silly faces, finished the job, then rushed home to watch the trailer proper.
It's crazy to think how the remake existed in my mind back then. The only footage we had was prerendered and we didn't know the game would be split into parts until December of that year. But the promise was made and the sky was the limit.
EDIT: Found the article -
https://www.siliconera.com/final-fantasy-vii-remake-is-coming-to-playstation-4/