One of Captain America: Brave New World's most hidden Easter eggs is an Incredible Hulk callback that you almost certainly won't catch on your first viewing

Marvel has trained us to look high and low for Easter eggs in its new releases, but it's unlikely you caught this incredible reference to 2008's The Incredible Hulk and Tim Blake Nelson's The Leader hiding throughout Captain America: Brave New World.

Spoilers for Captain America: Brave New World follow.

Throughout Sam Wilson's adventure, multiple assets are compromised by a potent combination of The Leader's brainwashing light show and a song, 'Mr. Blue' by The Fleetwoods.

As spotted by The Direct, Mr. Blue isn't just a catchy earworm to help bring down governments. No, it's actually a reference to Samuel Sterns/The Leader's codename when contacting Bruce Banner online in their search for a cure to The Incredible Hulk's gamma illness. Banner's codename, in case you were wondering, is the pitch-perfect 'Mr. Green'.

The reference goes deeper, too, once you flick through the rarely mentioned MCU tie-in comics – specifically the Avengers prelude titled Fury's Big Week – and notice that Black Widow helped take down Sterns in an incident that became known as 'Project Mr. Blue'.

Away from the MCU, Betty Ross occasionally uses the codename 'Mr. Blue' when attempting to contact Bruce – proving that it has a long, winding history that snakes all the way up to Marvel Phase 5 and The Leader's attempts to discredit President Ross (Harrison Ford) and his legacy.

Captain America: Brave New World is now in theaters.

For our verdict, you'll need the Captain America: Brave New World review. Then dive into our breakdown of the final act with our guides on the Captain America: Brave New World ending and the Captain America: Brave New World post-credits scene.