The Duchess of York, 63, is said to be in good spirits and recovering well after spending four days in intensive care in hospital following her exhausting ordeal.
It is believed mum-of-two Fergie needed round-the-clock monitoring after the anaesthetic took its toll during what friends confirmed was “successful” surgery.
She has returned home following the procedure at King Edward VII’s Hospital in Marylebone, central London, in which a breast was removed and reconstructed.
Friends say daughter Eugenie, 33, has “all but moved in” to Royal Lodge in Windsor, Berks, to look after her, while older child Beatrice, 34, has been “constantly on the phone”.
Fergie is also being supported by her former husband Prince Andrew, 63.
A palace insider said that plans for the family to move into nearby Frogmore Cottage, Harry and Meghan’s former home, have been “quietly shelved” for now.
King Charles, meanwhile, has written to his former sister-in-law to offer his “sincere wishes for a speedy recovery”.
Some well-wishers have sent flowers, one giant bouquet arriving by car.
Fergie, who is patron of the Teenage Cancer Trust, had been symptom-free before her cancer was diagnosed at a routine mammogram in May, as The Sun exclusively revealed.
Surgeon Christine Choy carried out the single mastectomy while colleague Stuart James reconstructed the breast using fat from Fergie’s stomach.
A friend of the duchess said: “The surgery took getting on for eight hours and was more involved than people think.
“Today, the message she wants to get out is that she’s very grateful and she feels very lucky to be alive.
“She wants to thank the two incredible surgeons Christine Choy and Stuart James who saved her life and all the medical team who worked tirelessly to help her.”
A source said Fergie, who was discharged from hospital last Sunday after six days of medical care, was lucky as her cancer was caught early.
They added: “Most people usually associate breast cancer with a lump but that’s not always the case.
“A lump can be detected by the patient, but this was a ‘shadow’, which can go undetected as it’s a wider spread of cancerous cells.
“In Sarah’s case, a biopsy was taken from the shadowy area of tissue and a few days later the results came back to confirm the diagnosis — breast cancer.”
