Each night, 18-year-old Ryan Wilcox sleeps under a portrait of himself dressed as Captain America — the pinnacle of human strength and endurance.

The Marvel Comics fan knows a thing or two about those heroic attributes. He is battling cancer for a second time in his life, and so when he recently received some disappointing news about his prognosis, his schoolmates rallied and called in the Avengers.

On Monday, the 70-pound teen answered his front door and was shocked at what he saw: Iron Man Robert Downey Jr. and Captain America Chris Evans had not only put aside their differences on how to save the world, they had teamed up with "Iron Man" star Gwyneth Paltrow to carry out a mission to lift Wilcox's spirits.

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"Hey what's up buddy?" Evans is heard as Wilcox shakes his head, doing a double take in a video taken by Paltrow outside his home in the San Diego suburb of El Cajon. "We were in the neighborhood and thought we'd cruise by."

"Hey guys," says Wilcox, wearing a T-shirt featuring Captain America's shield.

Paltrow, who plays Pepper Potts in the "Iron Man" films, hugged Wilcox's mom, as the other two stars plopped down on the carpeted living room floor. The celebrities spent an hour at the home, conversing with the teenager, like they were old friends, his mom, Amy Wilcox, said.

"She told me this is a gift from one mom to another mom," Amy Wilcox said. "She knew how happy it would be for me to see Ryan so happy."

Wearing a blue "Stark" hat with Downey's autograph on the bill, Wilcox was still reveling Tuesday in what he described as the best day of his life. He joked how his home was worth a billion dollars now and promised to preserve his game chair, where Downey sat at one point.

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"It was really cool hanging out with them. That really picked me up," said Wilcox, his voice barely above a whisper. "I'm going to get through this."

Captain America has been a symbol of strength for Wilcox. The film series has kept him going, keeping him distracted as he has undergone chemotherapy and bone marrow treatments during numerous hospital visits.

Wilcox was diagnosed with a rare blood cancer at the age of 16. His mother said the cancer may be the result of chemotherapy treatments he underwent to fight a brain tumor at the age of three.

In February 2015, he had to leave school because his immune system was too weak. He had a bone marrow transplant from his 14-year-old sister in April of that year, but he later had a relapse. Last month, the family was told the treatments are not working so far and his disease is progressing, his mother said.

"Ryan is fighting every single day," she said.

Thousands of students at Grossmont High School held a rally two weeks ago, chanting "Ryan Strong." Scores were dressed in red, white and blue in honor of his favorite superhero. Then a group of students made a plea on Facebook for the cast of "Captain America: Civil War" to visit Wilcox.

Evans responded within days of the posting with a video message telling Wilcox to "stay strong."

Evans on Monday signed the shield in the portrait of Wilcox dressed as Captain America above his bed. It reads: "Stay strong Brother!! Chris Evans. CAP."

Wilcox said Captain America inspires him because he "never gives up."

"Strength doesn't really come from muscle," Wilcox said, repeating the quote he coined that now is on T-shirts sold to raise funds for his cancer treatment. "It comes from your spirit, and your heart and love."