I'm probably not the first to notice this, but when Johnny Romita took over for Steve Ditko on Amazing Spiderman Stan Lee made it an important issue featuring Green Goblin, then when Gil Kane took over for Romita Stan Lee made it an important issue featuring the Green Goblin.
At any rate the key event in these two stories is that the Green Goblin learns Spiderman's secret identity. This is not unprecedented, by any means, especially when you consider the way the story is resolved.
As the story begins we learn that the Goblin is ready to strike. Peter is not in the best of health; he's battling a cold and while the family physician is treating him, the doc warns him that any shock could kill his aunt. The Goblin employs a gang which manages to hit Spidey with a gimmick that wipes out his spider-sense. Without his warning signal, Spiderman changes back into Peter Parker without realizing that he's being observed by his most deadly enemy.
The Goblin tails Peter back to his aunt's house, then attacks. He quickly subdues Parker and takes him back to a hideout by the wharfs. There he reveals himself as the father of Harry Osborn, a new classmate at Empire State who's already scrapped with Peter.
There follow several flashback sequences as we learn how Osborn, determined to be a success in business, and later crime, neglected his son along the way. We also get a recap of the prior Green Goblin-Spiderman battles. Finally they battle one last time. Spiderman manages to kayo the Goblin, and when Osborn regains consciousness, he has amnesia about the last several years.
Of course, in this sense, Stan Lee was just doing what comic writers had done since the 1940s. There was a tradition that if anybody discovered the hero's identity in the course of a story, he or she must either die or suffer amnesia before the story ends.
Unfortunately, a predictable by-product of this outcome was that the Green Goblin's appearances would become less frequent. Indeed, in the next five years, Gobby appeared only once, and that in the oversized Spectacular Spiderman; more frequent appearances would have made the amnesia result increasingly hard to believe.