He tweeted: "As I've told the BBC this evening, I'm not at all satisfied with the parameters they've set around their enquiry into the @BBCPanorama interview with Diana of 25 years ago tonight".
In the past few days some newspapers have carried criticism of Prince Harry for not "standing by" his brother, the Duke of Cambridge.
"Harry is getting regular updates and is aware of everything that is happening", the source told the BBC.
"You do not need a public statement to imagine how he is feeling privately, people know how much his mother means to him", the insider added.
"Sadly, some people are not just seeing this as a drive for truth, but also trying to use this as an opportunity to try to drive a wedge between the brothers", the person said.
"He has bravely spoken out in the past about loss and grief, and the enormous impact it has had on him".
In a statement emailed to CTVNews.ca on Thursday, Kensington Palace said Prince William "tentatively welcomed" the independent investigation led by Lord John Dyson, a former Supreme Court judge and one of the United Kingdom's most senior retired judges.
Charles Spencer previously accused the broadcaster of a "whitewash" and alleged he was shown "false bank statements" by Mr Bashir to help the reporter land the historic interview with the princess in 1995.
What will the investigation look at?
The BBC approved Lord Dyson's appointment on Wednesday after new Director General Tim Davie ordered an independent inquiry into allegations Mr Bashir fed Diana a string of lies and smears to obtain his exclusive interview with her.
'Lord Dyson must be free to examine every aspect of this matter, from 1995 to today, as he sees fit'.
The BBC has insisted that investigation has a sufficiently broad scope.
It was "incorrect" to suggest it would not cover the BBC's investigations at the time as this was "explicitly part of the remit", she said.
At the time, Princess Diana was separated from Prince Charles but not yet divorced.
The princess sent shockwaves through the monarchy with the interview, which included candid details about her marriage and the Prince of Wales's rumoured relationship with Camilla Parker-Bowles, his now wife.
The explosive Panorama interview famously featured Diana saying: "Well, there were three of us in this marriage, so it was a bit crowded".
A month later, the Queen urged the separated couple to divorce, which they did in 1996, a year before she died in a auto crash in Paris.