Si Cranstoun’s Sydenham-based family have uncovered a story about the rock and roll star’s great-grandfather who served in the First World War.

The crooner’s mother, Jackie Cranstoun, researched the family history after her son landed a million-pound record deal after busking on the streets for 20 years.

During the battle of Ypres, William Cranstoun helped save a wounded officer who had fallen from his horse.

He gave him medical attention while the German shells were falling around them both believing they were going to be hit at any second.

Gunner Cranstoun was awarded the Victory Medal for his efforts in what was dubbed one of the worst battles of the First World War, He also held the Mons Star and general service medal for bravery.

Si Cranstoun, who dedicated his performance on Chris Evans’ Breakfast Show last week to his great-grandfather, said he is incredibly proud of him.

He said: “The family have only just discovered this news and we are all really chuffed. This has given me a real sense of identity and I feel honoured that he has fought for us to have a free life and this has given me even greater inspiration for my music.”

The 38-year-old of Caterham, Sussex, started writing his own music aged 16 but hit the big time after a Warner music mogul signed him on the street more than two decades later last April. For years he struggled to make ends meet playing on the London streets – where Prime Minister Tony Blair once gave him 30p.

“My life is even busier than ever and hearing my songs played on the radio feels amazing,” he added.

Si’s album Modern Life is available to pre-order via iTunes.