The Earl explained how he introduced his sister to former BBC reporter Martin Bashir, before he realised he was "deceived" by him after being shown forged bank statements which suggested Diana was being betrayed by her staff.
WATCH:Charles Spencer says Princess Diana's grave is 'an oasis of calm'
Recalling his heartfelt apology, he wrote: "After Mr Bashir left, I said, 'I'm sorry, Duch – I've wasted your time. What that man has just said doesn't add up', and highlighted some of the discrepancies with what he'd told me before.
"She said, 'Don't worry, Carlos [her name for me], it doesn't matter – it was lovely to see you anyway.' "
Diana was raised at Althorp House
Charles also revealed he felt he was "groomed" by Mr. Bashir in order to get close to Diana in the weeks leading up to her first meeting with the reporter.
In the telling account, Charles claimed the "lies [Diana was exposed to] ensured that she came into that Panorama interview with a very skewed and false view of the situation she was in, having been lied to repeatedly.
"This led to her speaking in a way that set her on a course where she was without due protection when she needed it most."
The site of her grave was described as "an oasis of calm"
Diana sadly passed away two years after Charles first met with Mr. Bashir.
The Earl currently resides at Althorp house with his wife Karen. Diana's body is thought to be buried within the grounds. The special place where she was laid to rest was once described by her brother as "an oasis of calm."
Charles enjoys sharing candid updates with his fans from the beautiful Northamptonshire Estate where the late Princess grew up.
Charles is a doting father to two five lovely daughters Lady Kitty Spencer, Lady Amelia Spencer, Lady Charlotte Diana Spencer, Lady Eliza Spencer and Lady Lara Spencer.
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