Fantastic Four (1961 series) #320

In New York, the Thing is alone atop the Baxter Building when the Hulk suddenly drops on him (courtesy of a rocket pack loaned by Doom) with a mighty blow, knocking Ben to the street. The fight continues through the streets of New York, with the Hulk concerned about hiding his true identity from his foe, and into the sewers, as Doctor Doom watches from a place of concealment. The Thing clobbers the Hulk, frustrated that he isn’t finally beating the real Hulk, and as he is about to deliver the final blow, the combatants are interrupted by the sudden appearance of…the green, savage Hulk!?!