When star showbiz names go delving in their family tree for a TV ancestry show, there are often surprises and a few tears – but nobody has uncovered a skeleton in the cupboard like Derek Niemann.

For most of his life, Derek’s dad kept his early childhood hidden away from the world, his children, even, perhaps, from himself.

Though he had lived through the war in Nazi Germany, he never, ever, discussed it in front of anyone.

It wasn’t until Derek was 50 that he made the chilling discovery.

In his father’s own words: “I was at Dachau. Not as an inmate – I was one of the bad Germans. I used to tell people I was in Munich, but no, I was at Dachau.”

His dad was Rudolf Adolf August Martin Wilhelm Niemann and it was his grandfather Karl who had been an officer in the SS, attached to the slave labour camp, with his family and children living nearby.

A lifetime of unsettling hints and clues began to fall into place, and Derek set out to unearth the true story of an often contradictory family man and his involvement in one of the greatest horrors in human history.

Scots-born Derek is a nature writer and editor who has also written Birds in a Cage, the true story of POWs who overcame the hardships of imprisonment by watching birds, combines his twin passions for history and natural history.

He will be talking about his new book, A Nazi in the Family, at Letchworth’s David’s Bookshop in Eastcheap on Tuesday, October 6, at 7.30pm.

Tickets are £4, which can be deducted from the cost of the £14.99 hardback if you buy it on the night. Find out more at www.davids-bookshops.co.uk.