Prince Harry’s efforts to safeguard his wife and children have further strained his relationship with his father, King Charles.

When the Duke of Sussex, 39, visited the U.K. in May for the 10th anniversary of the Invictus Games, his father was conspicuously absent. Although the King’s busy schedule was cited as the reason, sources close to Harry hint at a deeper conflict. Harry sought to discuss his long-standing battle for security, a fight he believes Charles, 75, could influence. Buckingham Palace, however, denies that Charles has control over Harry’s security.

The family rift, which went public in 2020 when Harry and Meghan Markle stepped back from royal duties, has been marked by intense disputes and lingering tensions. Security remains the most contentious issue for Harry, according to insiders.

In February, father and son had a positive meeting following Charles’s cancer diagnosis. But since then, their communication has broken down. Those close to Harry reveal that the King no longer answers his son’s calls or letters. “He gets ‘unavailable right now,'” a friend of Harry’s shares. “His calls go unanswered, even when he reaches out about the King’s health.”

Amid this estrangement, Harry remains deeply worried about the safety of his wife and children, Prince Archie and Princess Lilibet. Sources say he has repeatedly sought his father’s help. “Harry is frightened and feels the only person who can do anything about it is his father,” a royal insider tells PEOPLE. Another source adds, “Harry is determined to protect his family at all costs.”

The issue has escalated. In the ITV documentary “Tabloids on Trial,” which aired in the U.K. on July 25, Prince Harry expressed his fear that negative press could incite violence against his wife. “All it takes is one lone actor,” he said, explaining why he hasn’t brought Meghan, 42, Archie, 5, and Lilibet, 3, back to the U.K.