The late Queen Mother was one of Britain's most instantly recognisable figures, but few of us have even heard of the Queen's mother-in-law, Princess Alice. But her life story almost defies belief.

A great granddaughter of Queen Victoria, Prince Philip's mother married into the Greek royal family, only to see the Greek monarchy overthrown by revolution.

Fleeing into exile, she suffered a severe nervous breakdown. She was locked away in mental hospitals and subjected to experimental treatments by psychiatrists, including Sigmund Freud.

The trauma had a shattering effect on Princess Alice's marriage and led to a fractured childhood for her only son, Prince Philip.

Philip's mother eventually fought her way back from mental illness, and became an unlikely hero of World War II, risking her life to hide a Jewish family from the Nazis.

When her son married the future Queen Elizabeth in 1948, Alice turned down the option of a cosy royal life. Instead she chose to dedicate herself to working with the poor in Greece, gave away all her possessions and even founded her own religious order.

Featuring exclusive interviews with family members and previously unseen archive footage, this film sheds new light on one of the royal family's most remarkable, but least known, personalities.