The ITV show's official Twitter account announced on Friday (1 April) that writer and broadcaster Denise had lost her battle with cancer.
A short statement read: "Such sad news – our friend and colleague Denise Robertson has lost her short but determined battle against cancer."
The show will pay full tribute to Denise on today's episode.
Denise revealed in February that she'd been diagnosed with pancreatic cancer, saying: "A persistent health issue turned into something quite a lot bigger."
In a statement at the time, she said: "It has come as a surprise to me and my family but we know many others have suffered and dealt with this condition and I don't plan to give up without a fight.
"My doctor is referring me for chemotherapy and hopefully that will start soon. I'd like to thank all the lovely viewers of This Morning who have been concerned about my health and I hope I'll be back on the sofa soon."
She had phoned into the studio on 3 March to thank viewers for their messages of support and give an update on her health.
Speaking from The Royal Marsden Hospital in London, she said: "Can I just say how much it's meant to me all the love and support that's come in from colleagues, the viewers, it really is the most enormous help. Believe me, it's a real lift."
Denise had appeared on This Morning since its first broadcast in 1983.