I highly recommend previous posts on this subject:

by /u/qed1 who shows that the ancient and medieval science already theorized that seasons would be inverted

and by /u/drylaw, who shows the work of mid-sixteenth century writer-scientist observing and explaining the phenomena

I myself have tried to show how did the realization of the inverted seasons evolve during European Age of Discovery in my post Did the first European explorers understand that the Southern Hemisphere experienced reversed seasons and why? What did they think about the so called Torrid zone?

I don't think it is really possible to answer who was the first to realize it and when, but as /u/qed1 demonstrate it was certainly deduced theoretically to be the case by (at least) the ancient Greeks and Romans