Willem Dafoe's return as Green Goblin was such a big secret even Tom Holland didn't know about it
The current Spider-Man actor found out on set after bumping into a cloaked Dafoe

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Spider-Man: No Way Home Screenshot: Marvel Studios
Marvel Studios always goes the extra mile to keep major spoilers hidden from fans and Spider-Man: No Way Home was turned into a whole spectacle of speculation. Andrew Garfield has been giving the performance of his life, denying that he’ll reprise his role as Spider-Man, as the movie is rumored to feature all three Spider-Mans. But at least one rumor is now confirmed: Willem Dafoe is back as the Green Goblin.
While Alfred Molina was already said to play Doc Ock again, Marvel had yet to officially say whether or not Dafoe would be behind the mask. At a fan event in Los Angeles last night, where the newest trailer premiered, it was finally revealed.