Alongside an old photo of herself and Shannen, Tori wrote on Instagram: "I don't have outward words yet, but WE knew and that's what matters."
The actress also emblazoned her post with several lines of broken-hearted emojis.
Other '90210' stars to pay tribute to Shannen included her Cindy Walsh actress Carol Potter, who noted that she was "shocked and saddened" at the passing of her on-screen daughter.
She wrote: "Shocked and saddened by news of Shannon Doherty's death. What a journey she has been on! Gone too soon. Throughout, she stayed true to herself and gave us an example of courage and perseverance in facing her own death. May she rest in peace." (sic)
Meanwhile, Jason Priestley - who played Shannen's on-screen twin brother Brandon on the teen drama series - remembered Shannen as "force of nature" as he sent his condolences to her loved ones.
He wrote: "Shocked and saddened to hear about the passing of my friend Shannen. She was a force of nature and I will miss her. Sending love and light to her family in this dark time."
The star underwent surgery towards the end of last year to remove a brain tumour she had named Bob and instead at the time that she head worked tirelessly to regain her motor skills and declared herself as "not a quitter".
She charted her health battles on the podcast 'Let's Be Clear with Shannen Doherty' and insisted as late as November 2023 that she "wasn't done" with living.
She said: "I'm not done with living. I'm not done with loving. I'm not done with creating. I'm not done with hopefully changing things for the better.
"I'm just not — I'm not done."
Celebrity news
90210's Tori Spelling 'doesn't have the words' to express how she feels about Shannen Doherty
The 51-year-old actress starred as Donna Martin on 'Beverly Hills, 90210' in the 1990s alongside Shannen - who passed away on Saturday (13.07.24) following a long battle with cancer - and took to social media with a brief message regarding her grief
