A convicted sex offender joined senior members of the Royal Family on their barge during the Diamond Jubilee pageant, it was revealed on Thursday.
Harbinder Singh Rana was invited onto the Spirit of Chartwell as a guest of the Prince of Wales - who was not aware of his criminal past.
Rana, from Walsall, West Midlands, stood trial in 1986 after posing as a doctor to carry out the attacks. He was sentenced to four years in jail after being convicted of five counts of indecent assault, 11 counts of assault causing actual bodily harm and one count of attempted assault.
He met Charles through his work with the Anglo Sikh Heritage Trail, which aims to promote awareness of the links between Sikhs and Britons. Rana is honorary director of the charity.
A Clarence House spokeswoman said: "Harbinder Singh was asked to take part in the pageant as he is a leading member of the Sikh community and someone who has done a lot of charitable work.
"Guests of the pageant including representatives from all major faith communities, spread across a number of key vessels - as with the Royal Family, who were present on a number of vessels. No, we did not know about his
Rana told the Daily Mirror that he did not commit the crimes, saying there had been a case of mistaken identity. He confirmed that he had not been asked about the matter before Sunday's pageant.
He told the newspaper his conviction was "very circumstantial" and added: "I was given the invitation and I attended. The fact that the Prince of Wales invited me clearly shows what I have done for the community since then."
A royal source said that he would not have been invited had anyone known of his convictions. Rana said he did not speak to the Queen or any other senior royal on the barge.
More than a million people attended the pageant on the River Thames which was hailed a success despite the cold conditions and persistent rain which deluged participants and public.