Tom Parker Bowles had been dating former journalist Alice Procope for almost two years before she died of cancer at the age of 42.
The mother-of-three died peacefully at home on March 17, seven months after she was diagnosed with the disease, according to the Daily Mail.
WATCH: Prince Charles films from inside living room at home with Duchess Camilla
Food writer Tom is said to be "devastated" by her death and was "blissfully happy" with Alice, who he began dating after splitting from his wife Sarah Buys in 2018.
The paper also reports that Alice's cancer diagnosis was "partly" delayed due to COVID-19 and wasn't discovered until last August, by which time "it was too late".
Alice was the granddaughter of the 2nd Viscount Ingleby and had three young children, Katherine, Wilfred and Georgia, with her estranged husband, Robert Procope, grandson of baronet Sir Robert Wigram.
Tom is very close to his mother and Prince Charles
Tom, whose father Andrew Parker Bowles is Camilla's first husband, is very close with Charles and previously said he has "always adored" his stepdad.
He told A Current Affair in 2015: "All you care about your parents is they're happy and my mother is exceptionally happy at the moment. I've always adored my stepfather; he's always been a kind and good and lovely man.
"He is a man of warmth, intelligence and humanity and I think if it ever happens, he will make a fantastic King."
Tom has written five cookbooks and won an award for his writings on British food in 2010. He has also presented a number of food shows and has appeared on MasterChef.
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