Carrie Fisher and Debbie Reynolds' Moving Relationship Shown in Heartbreaking New 'Bright Lights' Trailer

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Debbie Reynolds and Carrie Fisher were not only mother and daughter, but they were the best of friends.

HBO officially released the trailer for Debbie and Carrie's documentary, Bright Lights: Starring Carrie Fisher and Debbie Reynolds, which perfectly displays the touching relationship between the two Hollywood legends. Carrie constantly worries about her mother's health in the video, and describes their incredible bond.

"My mother, she'll forget she's not 35," Carrie says about Debbie's busy schedule. "Age is horrible for all of us, but she falls from a greater height."

WATCH: Joely Fisher Says Debbie Reynolds 'Would Not Last' Without Carrie Fisher, Reveals Their Last Conversation

"I'm my mom's best friend," she later comments. "Far more than I would ever want to, I know what my mother feels and wants."

The Singin' in the Rain star shows her sense of humor throughout the documentary, joking, "I share everything with my daughter ... especially the check."

Though she later gets serious about Carrie's well-known struggles with her mental health.

"Manic-depressive is a disease that was not diagnosed then, so nobody kind of knew what was going on with Carrie," she recalls.

"I went too fast, I was too much," Carrie acknowledges. "I couldn't handle it."

Carrie died at the age of 60 on Dec. 27 after suffering cardiac arrest while on a flight from London to Los Angeles. Debbie died just one day later after suffering a stroke. She was 84 years old.

Bright Lights
premieres January 7 at 8 p.m. on HBO.

WATCH: Todd Fisher Calls Carrie Fisher and Debbie Reynolds' Relationship 'a Beautiful Love Story'

Todd Fisher -- Carrie and Debbie's brother and son, respectively -- said that the two will be buried next to each other and "among friends" at Forest Lawn Memorial Park in an interview with 20/20 last week. Family friends Liberace and Bette Davis are also buried Forest Lawn.

"She didn't die of a broken heart," he also said of his mother. "She just left to be with Carrie."