The 51-year-old "Buffy the Vampire Slayer" creator made the shocking revelation at the screening of the 45-minute "Dr Horrible" tuner starring Neil Patrick Harris, Felicia Day and Nathan Fillion, reported Variety.
"Avengers" that released in 2012 grossed more than USD 600 million domestically alone.
"Dr Horrible," a musical about the titular super villain played by Harris, was conceived of by Whedon during the 2007-2008 writers strike.