Bear Grylls goes on an adventure with Who Do You Think You Are?

Some guests on the long-running genealogy programme seem to already know they’re going to have fascinating family histories.

For others, however, it can be a complete surprise (no offence, Josh Widdecombe, but who knew you would be descended from Henry VIII? And then, of course, there’s Danny Dyer to consider).

Tonight’s subject falls firmly in the former camp: the adventurer Bear Grylls, who has served in the SAS reserves, climbed to the summit of Mount Everest, paraglided over the Himalayas and been the youngest-ever Chief Scout.

As a wilderness expert he has visited some of the most hostile environments on earth, emerging (largely) unscathed; and he explains here that he has always displayed a tendency to “follow the path less trodden”.

So it comes as little surprise to learn that his family tree is full of fascinating figures; it’s clearly in the genes.

This becomes apparent from the off, when Bear delves into his army-serving paternal grandfather Ted Grylls’ old trunk – which is rather intriguingly full of documents marked ‘Top Secret’.

Ted trained to be an army officer in the 1920s, so Bear heads to Sandhurst Military Academy where Ted studied and developed a fascination with all things mechanical – especially tanks.

With help from the team at the British Tank Museum, Bear learns how Ted became one of the British Army’s biggest experts in armoured vehicles and tank warfare.

As an adviser to both the British and Americans on how to win on the battlefield, he even contributed to the success of the D-Day landings.

But it was Ted’s later job leading the ultra-secret organisation “T-Force” that helps Bear really understand the pressures his grandfather faced, and reveals clues about his character. It might also explain some of those “Top Secret” files…

T-Force were charged with identifying, tracing and sometimes even kidnapping Germany’s best scientists for interrogation by the Allies after the War, so Ted had to stay in Europe long after the conflict was over, working on a morally complex mission, far from his family.

Bear also wants to find out more about the life of his beloved other grandad Neville, and his father – Bear’s great-grandfather – Lionel Ford.

Happily, Lionel is revealed to have been a loving family man, and a progressive school headmaster who set about modernising Harrow. Finally, following his family line back several centuries, Bear is delighted to discover some Scottish ancestry – which might excuse his professed penchant for a kilt.

The ties to Scotland transpire to be quite impressive: it seems his 10-times great-grandfather was the Duke of Argyll, a man whose religious beliefs and devotion to Scotland cost him his head.

And at his last destination, we learn that his mother’s hopes of a royal connection might actually come true: at the Argyll Mausoleum, Bear discovers that his 21-times great-grandfather is none other than a famous Scottish king.