The comic icon is known for making brief appearances in Marvel Entertainment films such as Thor and Captain America: The First Avenger.
Lee told Collider: "The Avengers cameo that you will see, when that movie opens up, is possibly one of my best. And you know how good mine have been, but it is so funny. I can't tell you what it is 'cause they'd kill me, but it is funny."
He continued: "So is the Spider-Man one, by the way. They're deciding to make my cameos a little funnier. They know that's what brings the audiences in, of course, so they've gotta play them up."
Lee also spoke about his cameos in general, saying: "It's almost scary 'cause they just give me a date. They'll say, 'Stan, come over next Thursday for your cameo', but they don't tell me what it is.
"I go on the set and one minute before we're gonna shoot, the director says, 'Okay, Stan, this is what I want you to do'. So, I don't know what is expected of me, until I get there, but of course, I do it magnificently."
The Avengers (Marvel Avengers Assemble in the UK) opens in UK cinemas on April 26 and May 4 in the US.
The Amazing Spider-Man will be released on 3D, IMAX and conventional screens on July 3 worldwide.
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Watch the Avengers trailer below: