Watch: Tom Holland reveals original villain plan for Spider-Man: No Way Home
The British star told Yahoo Entertainment UK that initial plans would've seen director Jon Watts' film promoted as "a civil war between [Spider-Man] and Doctor Strange", keeping the multiverse element a secret.
Plot details for the anticipated threequel have been kept tightly under wraps for months, but we do know that the film sees villains from other Spider-Man franchises arrive in the wake of a botched spell by Doctor Strange, designed to cause people to forget that Peter Parker is Spider-Man.
Speculation continues to swirl around which other villains will appear and whether the plot could allow previous incarnations of Spider-Man — as played by Tobey Maguire and Andrew Garfield — to show up.
"We're pretty tired of constantly lying and deceiving people. I feel like conscience is weighing on me now. It's tough," said Holland.
Holland's co-star Zendaya — who plays Parker's girlfriend MJ — said it would have been "exhausting" if they had to keep all of the villains' identities secret.
Trailers for the movie have revealed numerous returning baddies, including Alfred Molina's Doc Ock from Spider-Man 2 and Willem Dafoe as the Green Goblin from the first Spider-Man film in 2002.
Holland said: "Remember when that was the initial marketing plan? The initial plan was to make the film seem like a civil war between myself and Doctor Strange and they were gonna keep everything a secret. That is impossible."
Zendaya added that she "loves" to look at the inventive theories fans have come up with for how the movie will play out.
"There's some things where I'm like 'why didn't we think of that?'," she said.
She added: "It's really cool and I think that's part of the excitement and the fun — the theories and the ideas and possibilities.
"There now is, because of the multiverse, literally an infinite amount of possibilities of what this film could be or could turn into. I think everybody should just go into it with no expectations and just have fun."
Holland said it was "crazy" to share scenes with the likes of Molina and Dafoe, having grown up as a fan of the original Spider-Man trilogy, directed by Sam Raimi.
"People would have off-days and be like 'Tom's fighting with Willem today, we have to come in and watch that'," he added.
"For me as well, I'd be doing scenes with these actors and fighting them or just working with them and they'd say 'cut' and I'd have a moment like when you're almost outside of your body looking at yourself.
"This is crazy. It was wild. The fight scene I had with Willem was just mind-blowing.
"I'm very lucky. I have a certain lens that only I can see. I'm a huge fan of both franchises, but I also get to play Spider-Man in my franchise.
"So I have a lens and a memory of the first time fighting Willem that is crazy. It is mental."
MJ looks set to take a more active role in proceedings in No Way Home, working with Peter and his friend Ned (Jacob Batalon) to try to fix the problems created by the errant magic.
"These films are so fun for me and I love being around everyone. I would still only have one line and be perfectly happy," said Zendaya.
She added: "I really enjoy being there and what's been cool this time is that I would come to set even on the days where I wasn't working just to watch.
"It's so cool to watch Jon work and to learn from him as a director. I don't know how his brain keeps all of this because I was extremely confused and I didn't have as much to think about as he did.
"And also, being able to do stunts with your friends and people that you love and have shared so much life with is way more fun."
Spider-Man: No Way Home will finally swing into UK cinemas on 15 December.
Watch: Trailer for Spider-Man: No Way Home