A nuclear one at that.
Ron and Dave are making the rounds, and sat down with IGN to talk some more Return to Monkey Island. There aren’t a whole lot of new information, but in case there was any doubt that EMI and TMI were still canon…
Despite being Monkey Island 3 both in terms of Gilbert’s history with his own series as well as chronologically, Gilbert and Grossman both say the decision to canonify the other Monkey Island games rather than ignore or dispose of them was an easy one. “Yes, they are canon,” Grossman said, with Gilbert adding, “Neither Dave nor I felt like we could throw them out. There are a lot of beloved games. We love things like Murray. Throwing them out seemed like a pointless thing to do.”
… consider it undoubted.
Now run and read the whole thing.
Source: IGN
I still think "the secret" of Monkey Island is a McGuffin.