Princess Anne was confronted by demonstrators outside Wadham College at Oxford University, where she had arrived for the Agricultural Economics Society Centenary Conference.
As she stepped out of a black car, protesters shouted questions about her brother's ties to convicted paedophile Jeffrey Epstein.
"Anne, how long have you known about Andrew and Epstein," one heckler called out, with another repeating the demand.
The questioning continued with shouts of "what did you know and when did you know it" and "when will you answer the question."
Princess Anne was heckled by member of Republic at Oxford University
|REPUBLIC/X
The Princess Royal made no response to the protesters and proceeded towards the college entrance accompanied by several bodyguards.
The protest was organised by anti-monarchy campaign group Republic, which shared footage of the incident online.
The group pointed to reports describing Anne as "sympathetic" towards Andrew Mountbatten-Windsor despite the serious allegations he faces.
According to Republic, the Princess Royal has reportedly remained close to her brother and allegedly offered him a place to stay at her Gatcombe Park estate following his removal from the royal lodge in Sandringham.
Activists had previously targeted Buckingham Palace last month, attaching placards to the gates demanding answers about the royal family's knowledge of Mountbatten-Windsor's activities.
Those placards displayed images including one showing the former prince crouched over an unidentified woman.
Princess Anne is one of a number of senior royals that have been heckled in recent months
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Andrew was taken into custody last month on suspicion of misconduct in public office connected to his former role as a government trade envoy, with allegations he shared confidential information with the late paedophile financier Epstein.
The release of more than three million documents relating to Epstein showed the former prince featuring prominently, including numerous photographs with the convicted sex offender.
Virginia Giuffre accused Mr Mountbatten-Windsor of sexually assaulting her three times when she was 17 years old.
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Despite a photograph showing them together, he has maintained he had no recollection of meeting Ms Giuffre, who took her own life last year.
He reached a £12million settlement with her in 2022, though police declined to launch a full investigation. He has always denied any wrongdoing.
Republic's chief executive Graham Smith previously told GB News: "The big question that the royals have to answer now is what they knew and when, and what we really need is not just bland statements from palace officials saying, yes, of course, justice must be seen to be done.
One photo from the Epstein files appeared to show Andrew with a woman | BENCLINTON"What we need is a direct statement to camera in front of journalists from Charles and William saying we are going to make sure that all the information is available, we're not going to get in the way, and we don't want anybody to feel that they should."
Andrew Mountbatten-Windsor has always strongly denied any wrongdoing, and there is no suggestion of any wrongdoing by Princess Anne.
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