It was a meeting of heroes - one a major Hollywood star, the other an eight-year-old boy from Scotland fighting to save the lives of his friends.

Avengers actor Robert Downey Jr. made special time at the weekend to spend a day with Aaron Hunter, from West Dunbartonshire, who suffers from a rare and life threatening condition.

The pair were finally united in London after a video appeal from Aaron went global following the loss of one of his friends due to the debilitating illness.

Begging Iron Man to help him and his friends find a cure, Aaron's heartbreaking video was shared by Robert Downey Jr's fans on a mass scale online until it drew the attention of the star himself.

When word reached him through various fan pages, the compassionate star surprised Aaron with a video call in character as Tony Stark.

It was a dream come true for Aaron and the Iron Man star went one step further to name Aaron's charity as the one he wants his own foundation to support.

Random Act Funding was founded by Robert Downey Jr. and Susan Downey with the mission to distribute kindness in the form of financial support at local, national and global levels.

Through it, the actor is offering fans the chance to attend the world premiere of Avengers: Infinity War with him in California on April 23, 2018.

The entry fee to the competition will be donated to Aaron's ROHHAD charity, set up to support children suffering from the syndrome and to help fund research into a cure.

ROHHAD is one of the rarest illnesses in the world. A life threatening condition which causes rapid weight gain and breathing problems in young children.

The chances of Aaron developing it were one in 73m.

The condition is terminal and children living with ROHHAD face a daily fight for survival.

Robert Downey Jr. made special arrangements to meet his new young friend during a visit to the UK.

The pair met up over the weekend to discuss their plans for Aaron's charity and on how they can make a difference in the lives of all children suffering from the condition.

Aaron's mother and father, Lisa and Ian Hunter, and his big sister Lauren, said Aaron was delighted, especially after a recent deterioration in his health.

In a post on Aaron's charity page, the family said that now "his big heart is full of hope".

"Our beautiful, brave boy and brother. This memory will never leave us, it has been magical," they wrote.

"We have never seen Aaron this happy until now. His big heart is full of hope and the best is yet to come with the help this will bring all of the children fighting ROHHAD.

"Special thanks to Robert Downey Jr. and Team Downey for their incredible support and promise to help. The hope that this has given all the families is immeasurable."

The pledge of support from Robert Downey Jr. through Random Act Funding will mean children like Aaron with his rare condition now have a chance of finding a cure through much needed medical research.

To Aaron's family and the families of other children with ROHHAD, Robert Downey Jr. is a hero - but so too is the little boy who started it all.

"Aaron we are so proud of you, your huge heart, your determination, your selflessness and belief that the world is full of heroes who will want to help your special friends," said his mother Lisa Hunter.

"We love you more than we could ever put into words."