The BBC has paid a "substantial sum" and apologised to Princess Diana's former private secretary over a 1995 interview found to have been obtained using deception, the UK broadcaster said on Thursday.

An independent report by senior judge John Dyson last year concluded that then BBC journalist Martin Bashir had deceived Diana's brother into helping to arrange the interview, in which she spoke candidly about her troubled marriage to Prince Charles.

"The BBC and Commander Patrick Jephson have reached a settlement following the publication of the Dyson report," the BBC said in a statement.

Jephson, who aided Diana from 1988 to 1996, reportedly said that Bashir "seduced and betrayed" her into doing the interview.

"The BBC accepts and acknowledges that serious harm was caused to Commander Jephson as a result of the circumstances in which the 1995 interview ... was obtained," the broadcaster said.

Dyson concluded that Bashir commissioned fake bank statements that falsely suggested some of Diana's closest aides were being paid by the security services to keep tabs on her.

He then showed them to Spencer in a successful bid to earn their trust and land the sensational sit-down, in which Diana admitted adultery with a former army officer, James Hewitt, and detailed Charles' affair with Camilla Parker Bowles.

"There were three of us in this marriage, so it was a bit crowded," Diana told Bashir in the programme, which was watched by a UK audience of nearly 23 million people.

The BBC "apologises unreservedly to Commander Jephson for the harm caused to him", has paid his legal costs and "a substantial sum in damages".

The broadcaster said Jephson intends to donate the damages to charity.

The royal couple formally divorced in 1996. Diana died in a high-speed car crash in Paris the following year aged 36.