I'm meeting a leading expert on the British intelligence services.

Professor Richard Aldrich has spent weeks unearthing a treasure trove of secret files from the National Archives, and personal diaries of former spies, which shines a new light on my grandfather's war.

Richard, this is a conversation I've really been looking forward to, because it's part of my family history which is sort of steeped in mystery.

-Your grandfather has a fascinating Second World War.

In March 1941, he's appointed as defense security officer for the Caribbean.

He's both MI5 officer, and also MI6 officer, for the whole region.

So he's spy and spy catcher -- if you like, both "Spooks" and James Bond.

He's based in Jamaica.

And he has a fascinating neighbor, because the governor of the Bahamas at that time is the Duke of Windsor.

-Wow.

So -- yeah.

So this is the -- the part that I'm most fascinated by.

Am I right in thinking he was sort of keeping an eye on the Duke?

-Absolutely, because the Duke of Windsor likes hanging out with millionaires who are close to the Nazis.

Actually, he used to hang out with Oswald Mosley, the leader of the British fascists.

And they tour Nazi Germany in 1937.

And, extraordinarily, they go to meet Hitler in his Alpine retreat.

This is the guy that your grandfather is sent to keep an eye on.

-Throughout 1941, the Windsors lobbied U.S. President Roosevelt to stay out of the war.

-[ALDRICH:] Edward and Wallis were the first celebrity couple.

You know, the American press are fascinated by this British king, who's given up his throne for this American woman.

But, Edward is saying Britain should stop fighting Germany.

There should be a peace deal.

-Interesting.

So my grandfather's job was to keep an eye on Edward, the abdicated king, report back on what he was doing, what he was-- who he was talking to.

Is that right?

-Yes.

And he's MI5 and MI6.

-Yeah.

-But there's also FBI, there's Special Branch.

There's 24-hour surveillance when they go to Florida.

It's not just the phones being tapped.

There are bugs in the rooms.

This is a massive operation.

-So he's a bit of a spy?

-Absolutely he is, yeah.

-Excellent.

And this is, this is -- this is an important spying... -You can categorically say that my grandfather was a spy?

-He absolutely was a spy.

And this is one of the most important-- -Brilliant.

-spying operations of 1940-- -We can stop there.

That's fine.

[both laughing]