Robert Downey Jr.'s on-screen persona Tony Stark, better known as Iron Man, might be pretty cool since he gets to fly around and beat bad guys in a suit of armour. But the actor who portrays him is definitely way cooler since he gets to use his superstar status to spread optimism and cheer up children who are having a rough time health-wise.

It all started when Instagram user Vicky Keytes (@envy_coatings) shared a photo of her seven-year-old son Daniel, a huge Downey fan, who is suffering from cystic fibrosis, a congenital disease where a victim's lungs, intestines and pancreas become clogged with thick mucus. There is no known cure for the disease.

"Daniel could really do with a little lift at the moment after a child at school has told him that all children with (cystic fibrosis) die," she writes. "If this reaches him and Daniel could get a reply I hope that it could help him through his stay in hospital as it is starting to take its toll on him."

Downey quickly got in touch with Vicky through his Instagram account (@robertdowneyjr). Dressed up as Tigger, the actor who portrays Iron Man said, "Mr. Stark here. This is for Daniel (@envy_coatings) who was having a rough day recently. When I'm in the dumps, I've found this little getup to be helpful. P.S. Would you like to come to the LA premiere of 'Captain America: Civil War' as my guest? If so, have your people call my people. All the best."

Vicky was overwhelmed with Downey's support and care for her son, and she promptly made a follow-up post: "I want to say a huge thank you to everyone that helped to make this possible and a massive thank you to @robertdowneyjr for Daniel's invite to join you in LA. We physically cannot believe it and can't ever imagine a way to thank everyone enough, I will keep everyone updated on the build up to the big day on Daniel's progress and his day to day going on's and of course his tuxedo fitting that he has asked for today as he wants to fit in like a real star (not that he is not the biggest star in my eyes). Thank you everyone, this is by far the best wake up call ever when I found Robert's reply (I was a blubbering wreck)."