Joan Collins Says Sister Jackie's Death 'Left a Void That Was Impossible to Fill' Despite Their 'Ups and Downs'

"Are we supposed to be endlessly devoted to each other, and never disagree or do anything that might upset the other, just because we’re sisters?" Joan wrote of their complicated relationship

Joan Collins is getting candid about her tumultuous “rivalry” with her sister Jackie Collins and the dear place she had in her heart.

In her new biography, Behind The Shoulder Pads: Tales I Tell My Friends, the Dynasty alum, 90, opens up about her complicated relationship with her late sister and how her death left her feeling incomplete.

“Although the press and gossipmongers have ruminated about the relationship between my sister Jackie and myself, I like to think it was simply normal ‘sibling rivalry,’” she wrote in an excerpt shared with PEOPLE. “It is quite common between brothers and sisters, including recently between Princes William and Harry, and don’t forget the Bouvier sisters.”

Related: Joan Collins Believes Her Late Sister Jackie Visits Her as a Fly 'All the Time'

The actress recalled how “talking heads” in various media outlets would report their “rivalry” when Joan pursued writing after Dynasty came to an end and Jackie, a best selling author, pursued acting.

She admitted she never thought her sister “would mind” her literary ventures as she often “encouraged her acting ambitions” and helped her connect with casting directors and other Hollywood executives.

Joan revealed she learned of her younger sister’s “festering” sense of “resentment” in her 2021 documentary, Lady Boss. In the film, Jackie claimed she hated being known as her “little sister” and living in her shadow.

“I had always been top of my class in English composition, essays and writing, so therefore it seemed quite natural to follow in my sisters’ footsteps, much as she had in mine. But, sadly, Jackie’s documentary revealed that she had resented being promoted as my ‘little sister’ in her film and theatre career.”

Related: Joan Collins on Sister Jackie's Death: 'I Am Completely Devastated'

Desperate to make a name for herself, Jackie “insisted” on being called by her married name, “Jackie Lerman.”

“However, she realized that she wouldn’t be able to sell books under that name, so ‘Jackie Collins’ she became and faced all the publicity as ‘Joan’s little sister,’” Joan continued.

“I told this to her and Oscar [her husband],” she wrote of her confrontation. “‘You’ve been Jackie Lerman for years because you didn’t want to be known as my sister. Do you realise that in all the interviews you do they are going to ask you about me?’ Oscar agreed but said, ‘We want the book to be a bestseller. It doesn’t matter how we do it.’”

Joan also revealed the distance between them only grew when she dated and married men Jackie never approved of. In particular, Jackie “hated” Joan's fourth husband Peter Holm and Joan wrote that her sister claimed she’d “never speak to me again” if they got married.

The sisters went through another “period of coolness” when Joan dated her “English boyfriend,” Robin Hurlstone, who was “often sarcastically rude to her, correcting her pronunciation and commenting on her taste.”

Because of this, Jackie didn’t attend Joan's wedding to her husband Percy. Though the duo “never confronted each other about our problems, and it was only when I married Percy and she grew to love him, that our rift finally healed.”

Related: Jackie Collins' One Hope for Her Legacy: 'I Want on My Gravestone "She Gave a Great Deal of People a Great Deal of Pleasure" '

“I cannot deny that, like all siblings, we had our spats of ups and downs (but we never became anywhere near as cataclysmic as the Windsor boys!). But there were hurts,” Joan wrote, recalling an incident when she needed a place to stay in Los Angeles but ended up staying at a hotel after Jackie never offered up her home.

The actress also shared other incidents like going to parties and never speaking to each other. Another altercation involved Jackie skipping their father’s funeral, which made Joan and her brother Bill “extremely upset.”

“None of these issues were ever discussed, nor, I’m convinced, did Jackie ever fully explain any of them to other people,” she wrote. “Yet why should she? Are we supposed to be endlessly devoted to each other, and never disagree or do anything that might upset the other, just because we’re sisters?”

Related: The Glamorous Life and Times of Jackie Collins

Joan continued, “No one – not our friends, not our closest family – will really know everything we shared together, our bond over an entire lifetime, and the deep abiding love that always existed between us and that I still feel.”

Despite their differences, “When Jackie died, Percy and I, like our brother Bill, Jackie’s three daughters, six grandchildren, three sons-in-law and countless other friends and family, were bereft.”

“Jackie was so loved and admired by so many that her death was headline news across the world. She even made the cover of People magazine – she would have loved that! We grieved and tried to comfort each other, but Jackie’s death left a void in all our lives that was impossible to fill,” she said.

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Behind the Shoulder Pads: Tales I Tell My Friends is available in the U.K. now, but doesn't hit bookshelves in the U.S. until Oct. 24.

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