The number of people who believe the Prince of Wales has made a positive contribution to the Royal Family has fallen in the run-up to the 20th anniversary of Diana, Princess of Wales's death.
A YouGov poll commissioned by the Press Association found that 36% of the British public think Charles has been beneficial to the monarchy, compared to 60% in 2013.
More than a quarter - 27% - think the longest-serving heir to the throne has had a negative impact on the royals, in contrast to just 15% four years ago.
The research also showed that only 14% of the British public want the Duchess of Cornwall to become Queen when Charles is King.
Most - 39% - think she should take the title of Princess Consort instead, while almost a third of Brits - 30% - believe she should not have any title at all.
Royal commentator Penny Junor suggested the public has still not forgiven the Prince for the breakdown of his marriage to Diana, and his standing had fallen because of the publicity surrounding the anniversary.
She expressed surprise at the findings, saying: "We've moved on 20 years. Charles's reputation, I thought, was completely rehabilitated.
"He's become a much happier, more relaxed and more confident Prince of Wales and I thought much more popular as a result."
The author of the Camilla biography The Duchess: The Untold Story described Charles as "the most extraordinary Prince of Wales", adding: "I think he has been visionary over the years, the issues he's tackled have all become mainstream thinking."
But she said: "He gets a hard time because his marriage failed. He's never been forgiven for that - because Diana blamed him and he never ever said a word.
"He's never explained what went on in his marriage. His view has always been that history will judge him. He knows that he did all he could to try and make his marriage work and he failed."
She added: "I do think it's a very difficult time for him. The question of Diana has always been a source of difficulty between him and his sons."
The Press Association-commissioned poll follows surveys by national newspapers which also found unfavourable public opinions towards Charles and Camilla.
A Sunday Express poll, conducted by Norstat, found 67% of those questioned did not support the Duchess taking the title of Queen when her husband becomes King, while an ICM poll for the Sun revealed 51% wanted the Duke of Cambridge to be the next monarch, while only 22% surveyed said Charles.
Media attention surrounding Charles's ex-wife Diana has mounted ahead of the milestone anniversary on August 31.
Channel 4 has screened controversial video footage of the late Princess, who was killed in a car crash in 1997, revealing how Diana alleged Charles spoke about wanting to have a mistress.
Harry and William took part in their own television tribute to Diana with ITV, but made no mention of their father.
The YouGov survey was conducted following the furore over the Channel 4 programme featuring Diana's videos but before it was broadcast.
It shows that just 8% think Charles has made a very positive contribution to the monarchy, compared to 22% four years ago, and 28% believe he has made a fairly positive contribution, down from 38%.
But 9% thought his impact was very negative, up from 6%, and 18% fairly negative, up from 9%. Nearly a third - 30% - thought he had made neither a positive nor negative contribution.
Supporters of the heir to the throne would point to the huge sum, said to be more than a billion pounds, he has raised for charity over the past decade, including funds for the work of his Prince's Trust which has been supporting disadvantaged young people for more than 40 years.
Outside of his charity work Charles' support for environmental causes is well known from his campaigns to save the world's rain forests and encourage nations to combat climate change, to his work with businesses, governments and other organisations to promote sustainable ways of living and working.
William came out top for being seen as having a positive contribution to the royal family - in comparison to Charles, Camilla, the Duchess of Cambridge and Harry.
Ranked in order, 78% thought William had a positive impact, Harry 77%, Kate 73%, Charles 36% and Camilla 18%.
Among the younger age groups - the 18 to 24-year-olds - Kate's positive approval rating was 53%, but with the over-65s, it was 81%.
William and Harry are also seen as beneficial to the royals by a large proportion of pensioners - with William considered to have made a positive impact by 83% and Harry 82%.
Only Harry - who left the Army to pursue his charitable causes - has increased his overall positive rating during the last four years, with the figure rising from 72% in 2013 to 77%
William dropped from 85% in 2013, ahead of the birth of Prince George, to 78%, and Kate from 79% to 73%.
Camilla fell from 28% seeing her as having a positive impact in 2013 to 18%.
But 37% felt she had a negative impact on the monarchy, with 19% saying fairly negative and 18% very negative. Some 36% said she had been neither positive nor negative.
Support for Camilla becoming Queen has fallen by two percentage points in the last two years, dropping from 16% in 2015 to 14% in 2017.
Of Camilla taking the title Queen, Ms Junor said: "Principally her value is in giving Charles the confidence to do his job. It doesn't matter a hoot actually what she's called."
When Camilla married Charles 12 years ago, aides said she intended to be known as Princess Consort instead when he is King.
But according to legal experts, unless there is change in the law, Camilla will technically become Queen no matter what title she actually uses.
She has most support for being Queen from men - with 17% backing her for the title, compared to 12% of women.
Clarence House and Kensington Palace declined to comment.
:: All figures, unless otherwise stated, are from YouGov Plc. Total sample size was 1,614 adults. Fieldwork was undertaken between August 2 - 3 2017. The survey was carried out online. The figures have been weighted and are representative of all GB adults (aged 18+).