Princess Diana once wished her sons, Prince William and Prince Harry, would communicate on a “deeper” level.

In November 1995, the late mom of two penned a two-page, never-before-seen letter to a fan named Michael Barratt, who had sent her a supportive letter following watching her explosive BBC Panorama interview.

In the letter, Diana shared “how touched she is by the contents and by his profound words, and in particular relates to his sentiments of self-knowledge and moving on in life,” according to the Reeman Dansie’s “Royalty, Antiques & Fine Art” auction, which is selling the correspondence.

The former Princess of Wales wrote that she hopes her interview — in which she confirmed the breakdown of her marriage to then-Prince Charles due to infidelity — would help other women in similar difficulties.

The auction house said Diana wrote about looking forward to the future and “sharing with and teaching William and Harry the importance of communication on a deeper level.”

She concluded the letter by thanking Barratt, writing, “With my best wishes, Yours sincerely, Diana.”

The letter — estimated to sell from $4,000 to $6,000 — comes with its original envelope, including Diana’s handwritten name and address.

Diana died in a car crash in Paris in August 1997. She was 36.

Last month, Christopher Andersen, author of “KATE! The Courage, Grace, and Power of the Woman Who Will Be Queen,” told Page Six in an exclusive interview that William and Harry had tension “ever since they were small children, wrestling in the back of the car.”

Andersen told us that it was “made very clear” to Harry that “he was lesser than” William and that “left a real mark on them and really kind of doomed their relationship, ultimately.”

Today, both Harry, 41, and William, 43, are no longer on speaking terms.

Things began getting rocky for the brothers when the Invictus Games founder and his wife, Meghan Markle, quit the royal family in 2020 and moved to North America with their son, Prince Archie.

Things got worse when Harry and the “Suits” actress, 44, accused the royal family of racism and released a Netflix series about their issues.

Then, in January 2023, Harry dropped his bombshell memoir, “Spare,” in which he alleged William physically attacked him over Markle.

However, the dad of two has made some strides with his father, King Charles, even having an almost-hour-long meeting with him last September.