When was Minato confirmed as Naruto's father

[Minator93]

All started from here

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[Xāvî1]

When he met Minato while he was trapped in Chibaku Tensei.

It was confirmed before that

 

[iSpyder]

I figured it out way before it was confirmed
Same way how I figured out obito was half zetsu and tobi before it was confirmed

 

[TheSyren]

i remember there was a video game for ps2 that had naruto and the yellow flash. and the yellow flash looked like naruto from a distance. so i just figured he was naruto. that was before i read the series and watched the anime.

 

[Kurama999]

End of Part 1 upon leaving Konoha, when J took him to the training.
Naruto used his fingers to form a picture frame of Minato head.