"Sarah is mortified. She has been shattered and broken by the past few days. She is very raw. But to her credit she has pulled herself together and carried on with her business commitments, promoting her children's books Helping Hands. Oprah likes the books and will ask her about them."
The "mea culpa" interview, which will last 10 minutes, is to be recorded tomorrow and aired on Tuesday in the US. Clips from it are likely to be shown around the world.
Oprah is famous for persuading her guests to open up and give no-hold-barred interviews. Naomi Campbell spoke about her short temper, while the McCanns talked movingly about their conviction that their missing daughter, Maddy, is still alive.
Producers from Oprah struck a deal with the duchess late last night after going to see her talk at a book trade fair in New York yesterday morning.
The duchess will fly back to London overnight tomorrow to be reunited with her family and discuss where she goes from here.
On landing on Saturday morning she will drive straight to Windsor, where she rents a room at Prince Andrew's Royal Lodge residence, and meet him and their daughters Beatrice, 21, and Eugenie, 20.
Eugenie is travelling down from Newcastle, where she is at university studying for end-of-first year exams next week.
She and Beatrice have been inundating their mother with supportive phone calls and texts, a royal source said.
Prince Andrew, who categorically denies knowing anything about the "cash for access", is said to have forgiven his former wife.
