Watch the moving trailer for Carrie Fisher and Debbie Reynolds' HBO documentary

Last month two of Hollywood's brightest stars were taken just a day apart, and as the world mourns the deaths of Carrie Fisher and her mother Debbie Reynolds, HBO has released the first trailer for their new documentary exploring the pair's relationship. Bright Lights: Starring Carrie Fisher and Debbie Reynolds was originally set to debut in March 2017, but its release has been brought forward following the death of the legendary screen stars last month. Stars Wars actress Fisher passed away on Tuesday December 27, four days after suffering a cardiac arrest on a flight from London to LA. Her mother Reynolds died just a day later after suffering suspected stroke at her son's home, where she was reportedly making arrangements for Fisher's funeral. “I’m my mom’s best friend,” Fisher explains in the trailer, which takes on added poignancy in the wake of December's tragic events. “Far more than I would ever want to, I know what my mother feels and wants.” The documentary also touches on Fisher's personal struggles and the mental health advocacy which made her an inspiration to so many. "Manic-depressive is a disease," Reynolds says. "[But] that was not diagnosed then. So nobody kind of knew what was going on with Carrie." Bother Reynolds and Fisher were unwavering allies of the LGBT community, with Fisher recently appearing as a presenter at the Attitude Awards in 2014. Reynolds, who shot to fame in classic 1952 musical Singin' In the Rain and was married three times, admitted in 2014 that "everyone" she dated during her Hollywood heyday was gay, and that she would fake relationships with closeted leading men to hide their sexuality from the press. Bright Lights: Starring Carrie Fisher and Debbie Reynolds premieres in the US this Saturday January 7 at 8pm on HBO. More stories: Tom Hardy wanted to go full-frontal in new BBC One drama 'Taboo' Make-up giant Maybelline just appointed its first-ever male ambassador