The secret ending is showing a skrull, implying that the next
Avengers movie, if there will be one, will implement or revolve
around the Secret War.
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If by "not the cartoon" you refer to the 1960s TV series The
Avengers featuring secret agent John Steed, it's doubtful we'll see
another attempt at remaking it after the disaster that was the 1998
Avengers movie.
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Pro-Registration or S.H.R.A. and the Secret Avengers
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The Avengers - 1961 Super Secret Cypher Snatch 7-3 was released
on:
USA: 30 September 1968
UK: 9 October 1968
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The Avengers Earth's Mightiest Heroes - 2010 Secret Invasion
2-12 was released on: