Princess Diana's famous 'Panorama' interview will feature in a new documentary

Diana - who died in a Paris car crash in 1997 - famously dec lared her marriage to Prince Charles felt "crowded" because "there were three of us" involved, referring to the heir-to-the-throne's alleged affair with now-wife Camilla, Duchess of Cornwall.

A source told The Sun newspaper's Bizarre TV column: "The documentary intends to look at the years leading up to the controversial interview, and the aftermath of discussing her relationship to the heir to the throne.

"It's obviously timed to coincide with the anniversary of the Panorama programme, not to mention airing just as Netflix drama, 'The Crown', also delves behind the scenes of Charles and Di's marriage.

"The show will make for particularly uncomfortable viewing for the royals and couldn't have come at a more difficult time for them."

Diana - who married Charles in 1981 and had sons Princes William and Harry with him - and her husband divorced nine months after she gave the interview.

The princess - who lost her HRH status after her divorce - went on to find love with Dodi Fayed, who also passed away in the crash, while Charles and Camilla married in 2005.

Meanwhile, the next series of 'The Crown' will feature the marriage between Charles and Diana and actor Josh O'Connor, who plays the prince, recently claimed his co-star Emma Corrin attracts the same attention that her alter ego did.

He said: "It's something we got really used to. Poor old Emma is so young and it's one of her first jobs.

"So, she's often getting caught by the cameras whereas a lot of old hands know how to run away and hide. There are a lot of images of Emma looking amazing and she's doing an incredible job playing Diana."