-Millions of our grandparents were caught up in conflicts that shaped the 20th century.
-"We'd finally been released.
"I was only about seven stone by this time.
"I'd thought we were all going to die."
Yeah, it gets you, doesn't it?
It really does.
-Now, four international stars retrace their family footsteps across the globe.
-Granddad was sitting with a gun with instructions to shoot.
That must been very difficult for my granddad.
That's going against every fatherly instinct.
They uncover their grandparents' extraordinary stories.
-Your grandmother was here in one of the most historic moments of the 20th century.
-Oh my goodness.
I never knew that.
-So my grandfather's job was to keep an eye on Edward the abdicated king?
He's MI-5 and MI-6.
-You can categorically say that my grandfather was a spy?
-He absolutely was a spy.
-[laughs] What was she doing at a castle?
[laughs] Why are we at a castle?
-I mean, that's mind-blowing.
That's her voice.
-They discover how their grandparents' experiences of war changed their own lives.
-We are memories passed down, experiences passed down.
Those traumas, those joys of his life, live in me somewhere.
-That's what you pass on to your grandchildren, that surviving spirit.
God, it's really got me.