Alongside wife Judy Finnigan, Richard hosted the ITV morning programme from 1988 to 2001, working with Denise during that time.
Today's episode, fronted by Eamonn Holmes and Ruth Langsford, paid tribute to the late agony aunt, with the show's former hosts calling in to pay their respects.
During his call, Richard said: "A very sad day, although as Phil [Schofield] said… it hasn't come as the blindsided shock of Ronnie Corbett's death."
The remark has been panned on Twitter, as one viewer said: "@richardm56 are you for real?! 'Her death isn't a surprise like Ronnie Corbett!' Shut up!!"
"Sad news on This Morning.... made super awkward by @richardm56," someone else said.
A third person raged: "Unnecessary comment from Richard Madeley on @itvthismorning still a shock to her friends and family wether it was expected or not."
"Has Richard Madeley's foot EVER ventured out of his mouth?" asked another viewer.
Richard had gone on to say: "She gave really wise counsel, not just over the phone lines but privately.
"She was certainly the best Agony Aunt in the business because she was the most genuine."
Fern Britton, Holly Willoughby and Phillip Schofield also phoned-in.
"She's a woman that I very much admired and one I'll never forget as a friend and a very beautiful woman that we would all like to aspire to be," Fern said.
Denise announced that she had been diagnosed with pancreatic cancer in mid-Febrary, and passed away at the Royal Marsden Hospital in London yesterday.
A statement released by her family read: "We send our gratitude to the many thousands of people who have sent messages of love, support and prayers during these difficult weeks, these sustained and delighted her measurably."