Watch: Brenda Edwards shares letter sent by King Charles III after death of son Jamal
The TV star's son Jamal - who founded online music platform SBTV and was also an ambassador for the Prince’s Trust - died suddenly in February aged 31.
A coroner later ruled the cause of death was cardiac arrhythmia following cocaine use.
As she and her fellow Loose Women panellists discussed the death of the Queen, Brenda read out a letter in which the King said Jamal had made an "enormous difference".
It started: "Dear Ms Edwards, I particularly wanted to write and say how desperately sorry I was to hear the tragic news about your dear son Jamal, and above all to send you my deepest sympathy.
"I can only begin to imagine what an immense and aching gap he will leave in your life and that of your daughter Tanisha, and my heart goes out to both of you, more than I can ever say."
Visibly upset, Brenda read on: "I shall never forget Jamal's support and dedication in helping with my Prince's Trust over the years. His commitment as an ambassador has made the most enormous difference to the Trust's work and has helped to change the lives of countless disadvantaged young people.
"Jamal was, I know, greatly respected and liked by my Trust's staff, supporters and young people who he met during the many years of his involvement."
The King also mentioned the "enormous legacy of achievement" left by Jamal, who was awarded an MBE in 2015 for services to music.
At one point, Brenda, 53, had to stop and compose herself before going on.
After taking some deep breaths, she read: "I have such fond memories of the times I met him and can ill afford in this country to lose someone as exceptionally special as your dear son."
The monarch ended the touching letter by saying: "I fear that this letter can only be hopelessly inadequate under such soul-destroying circumstances and will probably be of no comfort whatsoever in making your sense of anguish any easier to bear.
"But please know that you and your family are so very much in my thoughts and prayers at this saddest and most heartbreaking of times."
Viewers were moved and posted messages on Twitter saying it had them in tears.
"My heart breaks for you," one tweeted.
"What a beautiful letter to @brenda_edwards from #KingCharlesIII had me in tears," said another.
One posted: "How hard it must have been reading that incredibly sensitive, thoughtful & compassionate letter and how lovely it was that the now King took the time to write & send it to you."