Stevens and his filmmaker girlfriend, Alexis Bloom, were recruited to shoot a project about Debbie's retirement as she prepared for the final performances of her one-woman stage show in 2014, but the Short Circuit star reveals the Singin' in the Rain legend was initially perplexed by the idea of the movie.

"She didn't understand the concept of a documentary," he recalled to The Hollywood Reporter. "She literally asked for lines. 'What should I say?' Ultimately, she was doing it for Carrie, and Carrie was doing it for Debbie."

Like many fans, Stevens was left "shocked" by Carrie's sudden death on 27 December (16), four days after she suffered a massive heart attack, as it was her mum who had been struggling with ill health for some time.

Tragedy struck again a day later, on 28 December (16), when Debbie suffered a stroke and also passed away, aged 84.

Stevens and Bloom's documentary about the famous mother and daughter duo, Bright Lights: Starring Carrie Fisher and Debbie Reynolds, focuses on Debbie's poor health and how the Star Wars icon cared for her, but the director was amused by the mother-and-daughter duo's quirky relationship.

"One of the reasons we wanted to make the film together is we (had) just had our first kid, and we fell in love with their relationship, Carrie and Debbie and the mother-daughter relationship and actually the whole family dynamic," Stevens told U.S. breakfast show Today. "We want people to... cherish their relationships with their families (after watching the film)."

The film features lots of old home videos from the family's archives and while Stevens acknowledges it was a challenge to sift through the footage, he feels lucky to have been granted such access to their extraordinary lives.

Bright Lights will premiere on U.S. TV on Saturday (07Jan17), a day after a joint burial service is set to take place at Los Angeles' Forest Lawn Memorial Park on Friday (06Jan17).

A private memorial for the two actresses was held at Debbie's Beverly Hills estate on Thursday (06Jan17). Meryl Streep was among the attendees.

The Devil Wears Prada actress, who portrayed the lead character in 1990 film Postcards from the Edge - which was adapted from Carrie's semi-autobiographical book of the same name, has reportedly been approached to deliver the keynote eulogy at a planned public gathering in the near future.