The claims follow weeks of campaigning by Diana's brother Earl Spencer for an independent inquiry into how Bashir convinced Diana to participate in the interview.
That call for an investigation into Bashir's actions includes allegations against the interviewer and the BBC, who Earl Spencer alleges lied and committed deception to persuade the royal into the tell-all.
“While I knew that Martin Bashir used fake bank statements and other dishonesty… what I found out only two weeks ago… is that the BBC also knew," he tweeted this week. "Not only knew about it but that they covered it up.”
Earl Spencer also spoke with the Mail, alleging that Bashir told 32 lies to the royal, including that she was being spied on by the royal family and that MI6 had secretly recorded Prince Charles discussing the “end game.”
He also alleges that Bashir used fake bank statements to reportedly prove the palace was selling stories to the press.
The BBC has since pledged to hold a full independent investigation into how Bashir obtained the career-defining interview.
“The BBC is taking this very seriously and we want to get to the truth," said Tim Davie, the BBC's director-general. "We are in the process of commissioning a robust and independent investigation.”
Bashir is currently unable to answer questions as he reportedly underwent quadruple bypass surgery earlier this year and also contracted COVID-19.
According to Vanity Fair, Prince William and Harry are "following developments in the story closely."
