Made public in 2015 after a decade-long legal battle waged by The Guardian newspaper, they included the plight of the Patagonian Toothfish and his famous bugbear, modernist building schemes.
Charles's opposition to bold new design first grabbed public attention in 1984 when he likened plans for altering the National Gallery in London to adding a "monstrous carbuncle on the face of a much-loved and elegant friend".
The disclosure of the "black spider" letters sparked a backlash against the then-future king and concerns he was overstepping his role.
However, in a 2018 interview marking his 70th birthday, Charles insisted he never directly meddled in party politics and understood the difference between being Prince of Wales and monarch.
More recently, Charles has become embroiled in an alleged cash-for-honours scandal.
A series of newspaper revelations claimed his close aides coordinated work to grant a royal honour and even UK citizenship to a Saudi businessman who donated large sums to restoration projects of particular interest to Charles.
Michael Fawcett, his former valet who rose through the ranks to become chief executive of his charitable foundation, resigned in 2021 following the launch of an internal investigation into the accusations.
It was the latest claim to tarnish Fawcett -- and, by association, Charles.
In 2003, Fawcett resigned after being accused of bending palace rules and accepting valuable royal perks.
He was later cleared of allegations of financial misconduct over the sale of unwanted royal gifts, but an internal report found various members of Charles's household guilty of "serious failings".
