Hollywood star, Robert Downey Jnr, has donated a once-in-a-life-time auction prize to raise funds for Julia’s House.

The actor – known to millions as Iron Man – has offered one lucky winner the chance to join him on the red carpet at the world premiere of his new film - Marvel’s Avengers: Age of Ultron - along with a string of other goodies, including a helicopter flight over Los Angeles.

The funds raised will be a welcome boost to Julia’s House which wants to offer more families access to its support and has just announced plans to build a hospice in Wiltshire.

The charity raffle is being hosted by Omaze, an American organisation that supports charities and provides opportunities for anyone to pay $10 and enter a draw for unique celebrity experiences.

Like life, you can't win if you don't PLAY. Click here to carpe that diem: http://t.co/bRwfiaQonb https://t.co/83RhDUdUBO

— Robert Downey Jr (@RobertDowneyJr) March 2, 2015

There is no limit on the number of entries per person and the winner is selected randomly by computer.

Robert Downey Jnr became interested in Julia’s House after he attended a fundraising event at the home of film director and Julia’s House patron, Guy Ritchie.

Martin Edwards, CEO of Julia’s House, said: “We are so grateful to Robert Downey Junior for helping with our dream to increase our respite and end of life care and reach more children over a wider geographical area, principally by building a Wiltshire children’s hospice and extending our home care in the county.

“It’s amazing when someone in so much demand is so focused on giving something back. He’s our superhero - we love you Iron Man!”

To buy tickets, visit Omaze.com.