The Sky Sports presenter, who also presented Blue Peter, announced the news today – revealing that she had only been diagnosed with leukaemia three days earlier.
And hundreds of people have paid tribute – including some of the biggest names, and football clubs, in the industry.
“Simon, the thoughts of everybody at Norwich City are with yourself, Ethan and everyone else who knew and loved Gemma at this sad time, wrote Norwich City.
While ESPN football host Alison Bender added: “Oh Simon, I can’t begin to imagine the pain you are all suffering. I’m sending you all my love on this difficult day and strength to Ethan.”
Wolves Football Club also wrote: “So so sorry to read this Simon. Sincere condolences from everyone at Wolves. Our thoughts are with you and Ethan.”
The tributes have continued to pour in since the news was announced earlier today, with Match of the Day’s Steve Wilson sending his “heartfelt” sympathy to the presenter.
Antonio Carluccio has died, aged 80, on November 8 [Getty]
He wrote: “I’m not one to pray, but I know you will somehow find strength from somewhere.”
Simon announced the news on his Twitter page, writing: “Today I am crushed with indescribable pain.
“Just thee days after falling ill with Acute Myeloid Leukaemia, my dear wife Gemma passed away yesterday evening surrounded by her family and friends.”
He added: “If you are a prayer – pray for my boy Ethan. 8yrs, precious and in bits. Thank you.”
Acute myeloid leukaemia is a type of blood cancer that affects the bone marrow.
Simon told The Mirror that Gemma felt ill last week and visited her GP where she was advised to rest.
“She felt very unwell last weekend and we took her to the doctor’s three times, but three times they didn’t seem concerned,” he said.
“They just said to rest, but on Monday we took her to the Royal Berkshire Hospital in Reading.
“After lots of tests they diagnosed her with blood cancer but they didn’t know what.”
He added: “A few hours later we were rushed to Churchill Hospital in Oxford, to specialists. They are an incredible team.
“We knew that we were in one of the very best places in the country.”
The 44 year old said that she started chemotherapy on Tuesday night, and although she initially responded well, her condition quickly worsened.
“For the first couple of days she was responding well, but yesterday morning she went downhill very quickly. She had bleeding on the brain.
“I was told yesterday morning she would be gone in a few hours.”
She passed away later that day surrounded by her family and friends, including son Ethan.
“My little boy had a little time with her but she wasn’t able to speak to him,” he said. “She passed away just before 6pm last night.
“There was a real sense of peace. Today is the hardest pain I have ever felt ever.”
Simon added that his son has been asking for “his mummy back” for Christmas.
“I would say, I’m not blaming our doctors here,” he continued. “I would say if you’re worried about something and you’re not getting an answer from your doctor, push.
“Three times we went. We were even told Monday morning to try some different pills and rest. Twelve hours later she was being diagnosed with blood cancer. You have to push them.”