The success of "Big Hero 6" had moviegoers automatically assuming that Disney would come up with a sequel. But while Stan Lee had revealed that a "Big Hero 6" sequel is in the works, the House of Mouse has kept mum about it.

However, an Easter egg spotted in "Avengers: Age of Ultron" has had fans talking about the movie again and hoping that they would soon see Baymax and Hiro in a sequel soon.

According to Reddit user, Kalean, he saw a reference to the 2014 hit in one scene of the Avenger's sequel. The eagle-eyed Kalean said that in the scene where Tony Stark was preparing to face-off against Ultron and his army, the names of two A.I. programs could be seen clearly, that of J.A.C.O.S.T.A and T.A.D.A.S.H.I.

Kalean posits that J.A.C.O.S.T.A is a reference to the robot wife that Ultron created in the comics. The sentient robot wife eventually became a force for good. Of course, anyone who has watched "Big Hero 6" know that Tadashi is Hiro's older brother, the one who developed Baymax and encouraged Hiro to use his talents and build robots in San Fransokyo.

A lot of Marvel fans remain skeptical about the easter, especially since no confirmation or any comment has come from Marvel's camp yet. But some have pointed out that everything is connected in the Marvel Universe and that the plot for the superhero animation was inspired by a Marvel comic.

Speaking of plot, there have been rumblings that the plot for the sequel will reportedly be so different from the first movie. According to reports, the sequel will have a darker theme and will allegedly revolve around Hiro's brother. Tadashi is seemingly resurrected and comes back with great powers. He will eventually become Sunfire, a nefarious character who lost his memories and who will fight against the "Big Hero 6" team.

The rumors that the sequel will be darker were further bolstered by reports that a new toy line from Bandai show the Big 6 heroes' colorful costumes changed to black.

No release date has been given for "Big Hero 6" sequel. However, there are reports that the movie might be released in 2019.