Prince William In 'Pain' Over Estrangement From Prince Harry: Report

Prince William's estrangement from Prince Harry reportedly remains a source of "pain and hurt" for the Duke of Cambridge.

Prince William is "settled as a dad" and "thriving as a royal" as he celebrated his milestone 40th birthday this week, according to People's chief foreign correspondent Simon Perry, who has been covering the Duke of Cambridge for more than two decades.

However, those who know or have worked with Prince William feel "deep sadness" that the royal's partnership with his younger brother has been "lost," Perry wrote in a piece published Tuesday.

An unnamed close insider told the correspondent that the brothers' estrangement is "an ongoing sore that shows no sign of easing soon" and is a source of "pain and hurt" for both Prince William and their father Prince Charles.

Journalist Russell Myers, the royal editor of the Daily Mirror and co-host of the "Pod Save The Queen" podcast, also discussed where the siblings stand today during a recent appearance on the Australian morning talk show "Today Extra."

Prince William and Prince Harry's relationship is still "strained in the extreme at the moment," and the older royal shut down his brother's efforts to reconcile during the recent Platinum Jubilee celebrations, Myers claimed.

But while tensions between the brothers have not yet eased, Prince William has "plenty to be proud of" in terms of his work as a royal and his family, according to Perry.

The royal has managed to secure the "balance" between having a private family life with wife Kate Middleton and their three children -- Prince George, 8, Princess Charlotte, 7, and Prince Louis, 4 -- and sharing some of it with the public, the royal expert wrote.

Perry believes Prince William has found the "best partner" in Middleton and that the couple's 11-year marriage "has blossomed into one of the great modern royal partnerships."

The journalist also noted that Prince William and his wife have already begun teaching Prince George and Princess Charlotte about the royal duties they will someday take on.

Prince William recently helped his two eldest children "take some of the first steps that mirrored his own introduction to royal duty at a similar age" during the Cambridges' visit to Cardiff, Wales, on June 4 as part of the Jubilee festivities, Perry said.

Meanwhile, Middleton reportedly pulled out all the stops for her husband's milestone birthday this week.

An anonymous source told Us Weekly that the duchess organized an "intimate party with friends" as a "special birthday surprise" for Prince William.

The bash Middleton threw for Prince William wasn't an "over-the-top" event that cost "a fortune," with the future king and queen consort focusing on being "low-key," according to the insider.

The duchess' plans for his birthday reportedly also included a "trip to the coast" together.

Prince William has "no big hang-ups about turning 40" because the second in line to the British throne "looks at every passing year as an achievement" in his life, the insider said.