Earlier today, the synopsis for Thor: Ragnarok dropped and revealed a major factor about Hulk's involvement in the upcoming threequel.
According to the description, Thor "must survive a deadly gladatorial contest that pits him against his former ally and fellow Avenger – the Incredible Hulk."
On the pages of Planet Hulk, which will be lending elements of its story to Ragnarok, the Hulk becomes a gladiator in Sakaar. As he climbs the ranks in battle, more and more threatening foes are chosen to face him. Eventually, the Silver Surfer is unveiled to be his opponent. In a shocking set of panels, the big green rage monster is pitted against the cosmic anti-hero. Hulk describes his opponent to ones of his allies who had been accusing Surfer of have been painted silver.
"That's not paint,' Hulk said. "He's the Silver Surfer. He's my---"
"Friend," the Silver Surfer said, finishing Hulk's sentence, before delivering a surprise blow to the big guy's face.
Ultimately, the Hulk wins the fight, but the two Marvel characters end up collaborating (along with Korg, Meek, and other lower tier alien characters) to escape the coliseum in which they've been fighting.
The scene may be adapted for the big screen in a number of ways. One of those ways is by re-introducing Hulk to the MCU following his absence since Avengers: Age of Ultron and briefly following his battles and happy new life on Sakaar. Later on, when things seem to be going well, Thor is introduced as his opponent and the two characters (who already have quite an on-screen history) end up duking it out.
Otherwise, Thor may end up tossed into the fighting pit and the well-established Gladiator Hulk might make his Ragnarok debut as the surprise opponent.
Either way, seeing the two character finish each other's sentence with the word "friend" would be inarguably iconic.
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