Although the 62-year-old musician - who has undergone seven rounds of chemotherapy in the last 18 months in a bid to beat liver cancer - is so exhausted he is sleeping up to 14 hours a day, he has vowed to appear at the London Palladium for the charitable 'Coming Home' concert, in aid of British troops on February 13.
He said: "I'm looking forward to appearing if possible and being able to continue my support for our service men and women.
"We owe a debt of gratitude to the dedication and professionalism of our armed forces."
Although Robin received permission from his doctor to perform after a final medical exam on Friday (27.01.12), friends are shocked that he will be well enough to attend.
A source told the Daily Mirror newspaper: "Quite simply it is a miracle Robin is able to perform. He is still incredibly weak and sleeping up to 14 hours a day.
"Robin will be literally dragging himself out of bed to do this gig. He is passionate about the charity and wants to do his bit. Our soldiers are modern day heroes but as far as they are concerned, Robin's efforts against the odds are every bit as heroic. It'll be an incredibly emotional evening."
Robin recently revealed he believes he is winning the fight against liver cancer.
He said: "I've had a scare. But now I'm happy to say I'm nearly better. For more than 18 months, I have lived with an inflammation of the colon; then I was diagnosed with colon cancer, which spread to the liver. I have undergone chemotherapy, however, and the results, to quote my doctor, have been 'spectacular'. It's taken a toll but the strange thing is that I've never felt seriously ill."