The British actress’ younger sibling would have turned 80 yesterday after passing away just over two years ago aged 77.
Taking a moment to remember the successful novelist, Joan, 84, posted a picture of them both looking extremely glamorous.
Alongside the gorgeous snap, the Dynasty star wrote: “Happy Birthday to my wonderful sister Jackie. Missing you terribly. #lovingsister #family.”
Her fans quickly responded with messages of sympathy as one person wrote: “The What a loss she is!.. to you and your family Joan and to all of us fans…. RIP… lovely lady….Xx”
Another commented: “Soul mates forever !! Don’t be sad !! bestow your sister the honour by living your life to the full..we raise a glass to Jackie !!”
Jackie – who sold over 500 million copies of her novels – died following a six-year battle with breast cancer.
Joan’s older sister chose to keep her illness a secret and only told her about it two weeks before her death.
Appearing on This Morning last year, the Golden Globe winner opened up about her loss and admitted: “I cried for three or four months.
“I miss her terribly. I have talked about it. Grief is a process. I think I cried for three or four months, two or three times a day.
“Then you get over that and you accept it, but then you think, ‘why did it happen?'”