A revealing snapshot of Carrie Fisher and Debbie Reynolds

Last year was a sad one when it came to celebrity deaths, but few were more heartbreaking than the death of Carrie Fisher and her mother Debbie Reynolds within only a day of each other.

In a new HBO documentary, which was originally due to be aired later in the year but has been brought forward to next week, filmmakers Alexis Bloom and, Fisher's friend, Fisher Stevens, followed both mother and daughter in 2014 and 2015. The film was Carrie Fisher's idea, who wanted her mother's life and legacy preserved and shared with the public.

The resulting film, Bright Lights: Starring Carrie Fisher and Debbie Reynolds, is as sweetly intimate - and eye-opening - a portrait of two Hollywood megastars as fans could want. The two were living next door to each other and the film goes into their shared compound and follows their day-to-day lives as well as tackling everything from growing up in showbusiness, to Fisher's bipolar disorder to Reynolds's declining health. Here are some highlights:

1 How Carrie Fisher lost her virginity: Not only do we learn how Fisher came to have sex for the first time but how her mother attempted to manage the situation. Sat on the bed of a London hotel, she discusses the loss of her virginity with her friend, actor Griffin Dunne.

He also happened to be the man who took it, as a friendly act of unburdening her of something she didn't want anymore because she didn't want her boyfriend to know she was a virgin. But Reynolds, Fisher said, had a different idea. She offered to supervise her daughter's first time with a different man that she selected herself.

2 Why Carrie's voice broke her mother's heart: Something only occasionally seen on TV during Fisher's life was her singing. But she has sung in her mother's stage act since she was 13, and with parents like Debbie Reynolds and Eddie Fisher it's no real surprise that she has a great talent for singing.

Archive footage of a 15-year-old Fisher being beckoned on stage to sing Simon and Garfunkel's Bridge Over Troubled Water (made even more interesting by the fact that Fisher later married Paul Simon) is juxtaposed with Fisher telling the filmmakers that she broke her mother's heart by not becoming a nightclub singer.

"I guess she doesn't want to be Eddie and she doesn't want to be Debbie. She wants to be Carrie so she'll do it her own way," Reynolds says tearfully. "I love that voice, isn't that a great voice? I wish I had it."

But Fisher seems to sing regularly in her day-to-life. Stood in her bedroom, she treats the camera to a few lines of I'll Never Say No from her mother's film The Unsinkable Molly Brown. Later, the pair perform together on stage in Las Vegas. Fisher, being Fisher, modifies the lyrics of the same song to "I'll weep because I'm bi-polar/Today is tomorrow if you do too much blow."

3 'I'm going to stay on stage until I drop dead': Debbie Reynolds's failing health: Though she wanted to continue working until her death (at one point she says, "As George Burns says that I'm going to stay on stage until I drop dead and then I'm going to have myself stuffed like Trigger then I'll put me in a museum."), Reynolds struggled to walk by herself and would often use a mobility scooter to get around. And watching her mother's health begin to fail clearly weighs on Fisher.

At the 2015 Screen Actors' Guild Awards, Reynolds was honoured with a lifetime achievement award. Backstage, as preparations are made for the evening, Fisher attempts to ensure that her mother will be comfortable, and that she'll have somewhere to lie down because, as she tells the staff, "she doesn't have much physical energy". Tears soon follow.

4 Carrie Fisher's Coke problem: During filming Fisher was preparing to appear in the new Star Wars film, The Force Awakens. She's spoken frankly before about how the producers would insist that she lose weight before filming begins. Here we get to see it in action.

"They make them report on my weight. They take measurements. It's intense," she exclaims, as she impassively uses an elliptical machine, under the eye of a personal trainer. Later we see the trainer pouring her beloved Coca Cola, of which she drinks more than a dozen cans a day, down the sink.

5 Carrie hits a wall in China: "When she was 13 her personality changed. It's a constant battle. It takes all of us to assure her that she's loved and that won't get her. It's hard," says a quietly emotional Reynolds to the camera.

We old see footage of Fisher, while still a young woman, having a manic episode on the Great Wall of China. Later, in the modern day, we see her mood switch while watching the film Funny Girl.

"I should have been a pair of ragged claws scuttling across the floors of silent seas!" she cries, in the same tone as having an epiphany.

Then she switches to doleful: "You know what would be so cool? To get to the end of my personality and just lay in the sun. I have to watch a little of this. I'm sick of myself."

6 Debbie Reynolds was a professional till the end: Even though she can barely climb stairs, Reynolds insists on still performing her stage show, only occasionally making references to retirement.

"I think I only got nervous once when I performed in front of the Queen of England," she reveals. "I went over with Bob Hope to do a show and I did get a little nervous. The crown and the jewels kind of threw me a little bit."