Jamie Lee Curtis heartbrokenly announced on Saturday that her elder sister Kelly Curtis has died at the age of just 69.
They were both in Hollywood from the time of their birth, the daughters of Some Like It Hot star Tony Curtis and Psycho actress Janet Leigh.
Both of them followed their parents' footsteps into the acting profession, with Kelly starring in such films as the 1991 Italian horror picture The Devil's Daughter, directed by Dario Argento, whose previous work included the original Suspiria.
She also worked behind the scenes in showbiz, including as a production assistant on Jamie Lee's films Freaky Friday, Christmas with the Kranks and You Again.
Posting to Instagram on Saturday, Jamie Lee revealed that her sister died at home Saturday morning but refrained from disclosing the cause.
Hailing her sister's 'loving generosity' and 'fierce opinions,' the devastated Halloween star mourned the loss of her 'first friend' and 'lifelong' confidante.
The Daily Mail has contacted Curtis's representative for further comment.
Jamie Lee Curtis heartbrokenly announced on Saturday that her elder sister Kelly Curtis has died at the age of just 69; the pair are pictured in 2012
They were both famous from the time of their birth, the daughters of Some Like It Hot star Tony Curtis and Psycho actress Janet Leigh
'A warm aloha to my older sister, Kelly Lee Curtis. She passed away this morning. In her home. In nature. At peace,' wrote Jamie Lee.
'She was my first friend and lifelong confidant. She was jaw droppingly beautiful, and a talented actress. She played a mean game of hearts, collected turtles, loved her family, nature, music, thrifting, travel, Facebook, and Pokémon Go,' she added.
Kelly, Jamie Lee wrote lovingly, 'was proud of her Danish roots and Hungarian Jewish ancestry and was a devoted American patriot.'
Jamie Lee continued: 'She will be remembered for her loving generosity, fierce opinions, endless curiosity, unique style, and her powdered, almond, crescent cookies at Christmas, hence her name, Auntie Cookie.'
The True Lies actress recalled that 'Kelly always signed off any message or fare thee well with a Hungarian blessing…Isten Veled, God is with you.'
As such, Jamie Lee concluded her tribute by writing: 'Isten Veled to my sister of the sun and the moon, my Tai. I'll see you on down the line.'
Kelly was born in Santa Monica in 1956, two years before her movie star parents welcomed her little sister Jamie Lee into the world.
Behind the elegant facade presented by the Hollywood publicity shots of their supposed family idyll, the marriage between the girls' parents was dramatically disintegrating, ending in divorce when Kelly was only six.
Kelly starred in such films as the 1991 Italian horror picture The Devil's Daughter (pictured), directed by Dario Argento, whose previous work included the original Suspiria
Kelly (left) and Jamie Lee (right) are pictured in the 1980s with their mother (center), who primarily raised them after she and Tony Curtis divorced
In the 2000s Kelly worked for her elder sister, serving as production assistant on her films Freaky Friday, Christmas with the Kranks and You Again; pictured 2007
The devastated Halloween star mourned the loss of her 'first friend' and 'lifelong' confidante; the sisters are pictured at the 1994 premiere of Jamie Lee's film True Lies
Tony Curtis claimed in his memoirs that he finally moved out on an impulse after a particularly brutal fight at the end of which Janet, well-oiled with Scotch, swallowed a 'handful' of pills and he had to slap her back to get her to regurgitate them.
'Sad to say, Kelly and Jamie have always held it against me,' wrote Tony, adding that the girls' mother had what was then the customary full custody 'and I'm sure she filled their heads with all sorts of negative stories about me.'
Despite the sturm und drang of her upbringing, Kelly 'was always remarkably practical,' her father said, recalling that when she was four years old and saw a TV for the first time she sat down behind it and explained to her father that she 'was looking to see where the pictures and sounds were coming from.'
Having developed an early interest in the mechanics of showbiz, Kelly studied at the Lee Strasberg Theatre Institute, named for the chief of the Actors Studio.
She had made her movie debut at the age of two in her parents' movie The Vikings, and she acted sporadically in movies as an adult.
Kelly landed a cameo in the classic 1983 comedy Trading Places, starring Jamie Lee with Dan Aykroyd, Eddie Murphy and Don Ameche.
Her star turns including the 1987 adventure comedy Magic Sticks, which featured a young Samuel L. Jackson in the bit part of a homeless man.
In 1991 she played perhaps her best-remembered part - an American schoolteacher in Germany who is targeted by a Satanic cult bent on impregnating her with the antichrist, in the Italian horror movie The Devil's Daughter.
Kelly was born in Santa Monica in 1956, two years before her movie star parents welcomed her little sister Jamie Lee into the world; the family are pictured in 1959
Behind the glamorous facade presented by the Hollywood publicity shots of their family idyll, the marriage between the girls' parents was dramatically disintegrating; pictured 1960
The picture was directed by Dario Argento, the Italian 'Master of Horror' whose films included Suspiria, Deep Red and The Bird with the Crystal Plumage and whose daughter is the scandal-struck actress Asia Argento.
Kelly also guested on a variety of classic TV shows of the 1980s and 1990s, such as The Equalizer, Hunter, Star Trek: Deep Space Nine, The Sentinel and Judging Amy.
Her father reflected in his memoirs: 'Kelly wanted to be an actress, and she eventually had some changes to work in films, but it never made her truly happy.'
She acted in the theater as well and married playwright-cum-producer Scott Morfee in 1989, but the marriage fell apart and her stage career never resulted in stardom.
In the 2000s Kelly worked for her elder sister, serving as production assistant on three of her movies - the 2003 classic Freaky Friday co-starring Lindsay Lohan, the 2004 picture Christmas with the Kranks led by Jamie Lee and Tim Allen and the 2010 romantic comedy You Again featuring Kristen Bell and Sigourney Weaver.
Tony Curtis, who died at 85 in 2010, had paid his own fond homage to her in his book: 'Kelly is a remarkably generous and compassionate person, sweet and giving.'