-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." Oh, God! Yeah, it gets you, doesn't it? -It does. -It does. 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? -Yes. 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.