In the summer of 2016, I had the rare privilege of arranging and witnessing a close encounter of a remarkable kind between an icon of science fiction and a genius of science – William Shatner and Stephen Hawking.

Prof. Hawking's home on a leafy street in Cambridge, England, was the last stop on a multicountry whirlwind tour during which Mr. Shatner engaged in conversation with the brightest and most creative minds on the planet, asking them where we will be 250 years from now – in the era of Star Trek – in our quest to understand the mysteries of the universe. The payoff for our documentary, The Truth Is in the Stars, was Mr. Shatner's interview with Prof. Hawking, one of the greatest minds of our time.

During my career in the film and television industry, I have had the chance to meet and rub shoulders with many people in the spotlight, but for both Mr. Shatner and me, the opportunity to spend a day in the presence of Prof. Hawking was likely the closest we will ever come to a revelatory experience.

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Yet it was an experience that almost didn't happen.

Although he appeared as himself in many popular shows and spoke at science conferences and events, Prof. Hawking rarely granted one-on-one interviews, especially in recent years. Given his reliance on the now-famous computerized voice synthesizer (activated by a mouse controlled by his cheek muscle) and his declining health, he was only able to write one word per minute. There were also concerns that our interview might be too fatiguing, and we were advised that it could be called off at the last minute.

But there were two factors working in our favour. Everywhere he goes, Mr. Shatner is approached by people who tell him that he was their inspiration for becoming an astronaut, an astrophysicist or some other scientific pursuit. He is a recipient of NASA's Distinguished Public Service Medal, the highest award bestowed by the agency to non-government personnel. Yet he had never had the opportunity to meet Prof. Hawking.

Prof. Hawking was a huge fan of Star Trek, even appearing as himself in an episode of Star Trek: The Next Generation, and had always dreamed of meeting Mr. Shatner. As it turned out, Mr. Shatner was an inspiration for Prof. Hawking. And thus, the stars were aligned.

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In order to minimize the strain, Prof. Hawking's team had limited us to six questions. We had a maximum of one hour, and the interview would take place at Prof. Hawking's office at Cambridge University.

In early July, I travelled to Cambridge and sat with Prof. Hawking at his kitchen table as I reviewed our proposed questions and presented an overview of the film. It would take him six weeks to compose his answers. And instead of filming at his office, he wanted to invite Mr. Shatner into his home.

Finally, in mid-August, the momentous day arrived. Mr. Shatner had arrived the day before on a direct flight from Los Angeles. Despite his own travel fatigue, he was energized. But first, there was a punting trip down the River Cam, during which he was pursued by paparazzi as we filmed, then a reflective moment in King's College Chapel before making the short trip to Prof. Hawking's home, where, with cameras rolling, the professor welcomed his new friend with the words: "Greetings, Captain Kirk!"

The backdrop was Prof. Hawking's library, adorned with photos and awards from his career. There was a photograph of him floating around with an apple in the so-called "Vomit Comet," an airplane that simulates zero gravity, and another with actor Eddie Redmayne, who portrayed him in the film The Theory of Everything – all evidence of a rich and rewarding life.

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Mr. Shatner's conversation with Prof. Hawking stretched for most of the afternoon. They talked about aliens, black holes, immortality, the connection between science fiction and science fact and Prof. Hawking's quest to find the single unifying theory that defines the universe. But most notably, there was humour and plenty of laughs on both sides. They pondered the possibility of one day sitting next to each other on Virgin Galactic's first flight into space. Prof. Hawking caught Mr. Shatner off guard with questions of his own – "What was your favourite alien on Star Trek?" – and ended the interview in true director fashion with "That's a wrap!"

I was touched by Prof. Hawking's love of life. Here was a man who at 21 was given only a short time to live and yet defied the odds and achieved great things during a long and productive life.

As our crew was packing up to leave, Prof. Hawking's voice computer came to life again, asking Mr. Shatner to stay for dinner – a very exclusive invitation that he warmly accepted. Later, in the courtyard of Prof. Hawking's home, Mr. Shatner was clearly moved. "It was like meeting a holy man … what a remembrance I'll have," he said.

In that episode of Star Trek: The Next Generation, Prof. Hawking sits at a poker table with Sir Isaac Newton and Albert Einstein, two scientists who have been immortalized by their achievements. With his passing, he joins that elite club of iconic figures whose legacy lives on for generations.

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Craig Thompson is a filmmaker, writer and producer based in Stratford, Ont.