United Kingdom, Sept. 27 -- Charles Spencer has revealed his enduring regret over Princess Diana - admitting he wonders whether he could have done more to protect his sister as she struggled with the extraordinary pressures of public life.

The 62-year-old has spoken about Diana in a series of interviews accompanying his newly released memoir, Swan Song: Diana, My Sister, as the 30th anniversary of her death approaches next year.

Speaking to People at Althorp, the Spencer family estate in Northamptonshire where Diana is buried, Charles said he had helped his sister during her final years but still questions whether he should have intervened more.

He admitted: "Could I have done more to help her with her public life? I probably could." ...