Mrs Wilson star Ruth Wilson on her grandad – the bigamist MI6 agent: "I wish I could have him round for dinner"

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Ruth never got a chance to meet her grandfather in person, as he died of a heart attack almost two decades before she was born.

Immediately after his death, his wife Alison (Ruth's grandmother) discovered – to her horror – that she was not the "official widow." The other Mrs Wilson had three children with Alec, and she also had no idea that Alison or her two sons even existed. Alec had pulled off a remarkable double life.

Even more extraordinarily (spoiler alert!), after Alison's death in 2005 it emerged that Alexander Wilson was actually married to FOUR women with seven children between them. A prolific novelist and writer, he served in the First World War, spent several years living in India, and joined MI6 – although the details of his work are tricky to confirm, especially given how many lies he told to maintain his juggling act.

Written by Anna Symon, the three-part BBC drama is partly based on Alison's typewritten memoir, which Ruth first read when she was 15. It stars Iain Glen as Alexander Wilson, who plays the role with sincere charm.

"When I first found out the story I was like, 'Oh my god what a legend!' I was like, 'Wow what a guy! How did he get away with it?'" Ruth says, putting on a funny voice. "I was amazed that that existed in our family, in our very ordinary family."

But taking on the role of Alison made her think deeply about her own grandmother's heartbreak.

"Actually playing my grandmother, I was like, 'No, what a s***'," she jokes. "Certainly during filming, because I was inside my grandmother's skin, I was like: this guy, I hate him. How could he do this? There was definitely moments of that."

You can understand her ambivalence. After all, Alexander's children – including her father Nigel – remember him fondly. And although it's possible that Alec was lying about going undercover for MI6 as a cover-up for his multiple lives, it is also possible that he was secretly doing vital work for his country.

She reflects: "I think nothing's black and white, and I think the reaction of the kids and the way they keep talking about him – and actually also the way they've been brought up, not only is that a testament to him, it's a testament to the women, and they all brought up their kids amazingly well. And the fact that they all have this shared love of creativity and language and they're just so open with each other - that for me is a testament to all the parents.

"So yeah, I did have mixed feelings, and I keep having them."

Ruth sees Alec as a "deep soul" who was "a really good dad" and ultimately a "gentle person." But he was also "mysterious and unknowable," which makes him hard to pinpoint.

"I think he remains, for all of us, a construction of memories of him," she says. "There's no real written piece from him. You've got his novels, but we don't have anything personal that he's written that you'd go: 'Oh that's the key to who he is.' It's everyone's memory of who he is."

As for playing Alison, Ruth says acting in the drama has given her a greater understanding of the person her grandmother became. Deeply religious, she was "quite guarded," and "wasn't very open" – except in her passionate and heartfelt memoir, which she left as her legacy.

"It was an extraordinary experience, and perhaps the most profound experience of my life, to be inside that woman," she says.

"People say to me, 'Who was your grandmother?' when I say I've made a drama about her.

"And I'm like, well she wasn't anyone famous and she lived an ordinary life... but she had an extraordinary journey."

This article was originally published in November 2018