Our insider added: “Kate and William are usually on the same page, but Harry has always been a sensitive subject.
“William started to feel like Kate wasn’t setting clear boundaries, and that caused strain.
“She came to see that trying to fix something beyond her control wasn’t worth putting her marriage under pressure.”
The decision comes as Kate continues her gradual return to public life following her cancer diagnosis and treatment earlier this year.
Last week, she pulled out of an appearance at Royal Ascot after attending Trooping the Colour and a visit to the V&A East Storehouse museum, prioritizing her health and recovery.
Sources say Kate had hoped to see Harry during his visit to London in May, when he appeared in court seeking to overturn the UK government’s refusal to provide state-funded security.
But those plans were quietly shelved.
“The timing just wasn’t right,” our source said. “Tensions were running high, and William was firmly against it.”
In a BBC interview following his failed legal bid in his security bust-up, Harry blamed his cancer-stricken father King Charles, 76, for the decision, and also moaned: “He won’t speak to me because of this security stuff, but it would be nice to reconcile.
“I don’t know how much longer my father has.”
