Yes and this accusation was used against Diana by one of Charles's powerful friends, when she was literally in the middle of minefield in Angola drawing attention to the Red Cross campaign against land mines.
It's a misogynistic tactic powerful men have been using against their ex wives for years - to call them "hysterical" or "unstable" in order to damage their credibility.
According to the Irish Times,
"The finger of suspicion pointed briefly at the Armed Forces Minister Sir Nicholas Soames. He quickly denied involvement and suspicion eventually alighted on Junior Defence Minister, Earl Howe.
He [Soames] admitted to lunching with two journalists at the Simply Nico restaurant, near parliament, but insisted he did not recognise the comments which appeared later in the Times and Daily Telegraph."
Apparently Howes later distanced himself from the comments.
In other words Howe "probably" took the fall for Soames, the Armed Forces Minister at the time - we don't know for sure - but Soames was a courtier at Buckingham Palace (an equerry to Charles) and had been a friend of Charles's since their teenage years. Charles was best man at Soames's first wedding.
Even John Major, the Prime Minister at the time, had to get involved to warn Nicolas Soames against bad-mouthing Diana in the Commons https://www.independent.co.uk/news/pm-ticks-off-soames-for-jibe-at-diana-1583354.html
And a threatening phone call from Soames to Diana was spoken about at the UK inquest in to her death.
Soames also spoke publicly about Diana's "mental instability and paranoia" which he later apologised for "because he wasn't a psychiatrist" and "he should not have got involved".
Remember that Diana, post divorce, had recovered from bulimia and was much happier away from the R. Any paranoia she may have felt was exacerbated by the activities of Martin Bashir who organised the faking of 72 documents to win over her trust. Her private secretary, who worked with her for eight years on her charity work, found her "good humoured, professional, and down to earth".
I think all of this is important because it speaks to the fact that Charles has allegedly used tactics such as allegedly using friends to brief against ex-members of the Royal Family with whom he is no longer on good terms. So the issue is still live! Of course Soames, if he was the culprit, could have acted independently but as it involved such a high profile individual, and he was a government Minister at the time, I think it's unlikely.