The actors behind some of Marvel’s most iconic superheroes are banding together to share their support for a British youngster recovering from heart surgery.

It all began when Ivan Hollingsworth shared a challenge on Twitter, on behalf of his son Seb.

“How do we get a @MarvelStudios Superhero to send a message to our Heart Hero Seb,” he wrote. “Recovering from open heart surgery and just so damn brave! Long shot I acknowledge, but I think he deserves it! Who’s up for the challenge?”

It didn’t take long for Marvel stars to respond, including Mark Ruffalo, a.k.a. Hulk.

“I think we have some competition for the strongest Avenger, @chrishemsworth,” Ruffalo tweeted, tagging his fellow Avenger. “Get well soon, Seb!”

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Hemsworth quickly responded. “The strongest Avenger by far,” he wrote, adding, “You are my heart hero, Seb.”

“Deadpool” star Ryan Reynolds also responded, telling Hollingsworth to check his DMs, and to “give it an hour.”

Hollingsworth then shared a video of Seb watching the personalized video message Reynolds had sent.

Seb also received a shoutout from Nick Fury himself, Samuel L. Jackson.

Also responding was “Captain Marvel” star Brie Larson, who wrote, “Seb, welcome to The Avengers,” signing the message with her superhero moniker.

Seb, who’s now at home recovering, shared his thanks in a video message his dad shared on Twitter.