Prince Harry, Prince William and never-ending sibling rivalry

No one quite grinds your gears like a sibling. But when you're a member of the royal family – and easy tabloid fodder – the pressure never lets up, and tensions are bound to erupt.

Look no further than Prince Harry's press tour surrounding his new memoir, "Spare," out Tuesday, which details life after his mother Princess Diana's death, his time in the military, his marriage to Meghan and his departure as a senior member of the House of Windsor.

But details of the fractured relationship between Harry and Prince William have turned many a head. A pair thought to be inseparable were anything but, Harry says

Healthy sibling relationships are built on mutual respect, and research shows they are an indicator of overall emotional well-being. That's because siblings relationships often outlast any other relationship in your life: romantic partners come into your life at a later age and parents often predecease their children. Siblings are with each other for life.

So what happens when those relationships crumble?

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Prince Harry, Prince William feud, explained

Prince Harry has detailed how his relationship with Prince William became strained over time. Among the recent revelations:

• Harry told Anderson Cooper in a 60 Minutes interview that William didn't want to be seen with him at school after their mom died. "No, no, no, when we're at school we don't know each other," William told Harry, he claims.

• William was not pleased with Harry and Meghan's relationship from the start. Tensions grew between the couple and William and his wife Duchess (now Princess) Kate, which led to a physical altercation in 2019: "His frustrations were growing, and growing, and growing. He was shouting at me. I was shouting back at him. It wasn't nice. It wasn't pleasant at all. And he snapped. And he pushed me to the floor," Harry says.

• The pair haven't spoken in a long time, though they walked together behind their grandmother Queen Elizabeth II's casket as they did for their mother more than 25 years ago.

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Why sibling relationships are complicated

The reason behind a sibling feud is hardly what matters most.

Research shows the sibling relationship is crucial to emotional well-being. The Harvard Study of Adult Development shows a close relationship with a sibling during the college years is the most reliable indicator of emotional health at age 65 – more influential than childhood closeness to parents, parental divorce, marriages and career.

Still, sibling rivalry isn't uncommon.

"It is natural for siblings to have some degree of rivalry and it should be expected. After all, kids are competing for resources within the family in terms of attention from parents and other needs and wants," says Laura Petiford, a licensed marriage and family therapist.

But that doesn't mean the relationships always go smoothly. Several factors can lead to the deterioration of a sibling relationship, though "it’s time to get help when the conflict is pervasive, occurring more days than not, and interfering with family functioning," Petiford adds.

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Family trauma, differences in political views, addiction and mental health struggles can challenge sibling relationships. Ruptures also can occur when a sibling breaks from the family identity, such as marrying someone the family doesn't approve of.

In the case of William and Harry, "the brothers both experienced the death of their mother, which is a deeply traumatizing event," Fern Schumer Chapman, author of "Brothers, Sisters, Strangers: Sibling Estrangement and the Road to Reconciliation," previously told USA TODAY. "A second risk factor is parental favoritism, and the monarchy presents the ultimate in favoritism, since William's going to become king and Harry will always be relegated to a supporting role. The monarchy is also notoriously bad at resolving personal problems. ... And Harry married far outside the family identity."

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How to repair sibling relationships

• Bear in mind that relationships ebb and flow. "A healthy sibling relationship, like any strong friendship, is characterized by love, respect, concern, consistency and reciprocity," says Chapman. "Siblings should expect to have conflicts, but in a healthy relationship, they feel confident that there will be repair and forgiveness." Plus, "as with any relationship there can be periods of closeness and distance. As adults, presumably there is more ability to reason and work through disagreements however many things can interfere with that actually occurring," Petiford adds.

• Accept not all relationships can be fixed. Some sibling relationships are too toxic to repair, and others will need to remain limited. Dealing with a difficult sibling may mean establishing firm boundaries. For estranged siblings, reconciliation is possible only if all family members feel safe and there isn't a risk of further abuse or retraumatization.

• Therapy, therapy, therapy. Chapman says early conversations during reconciliation are best facilitated by a therapist. Siblings will have to listen without interrupting or challenging each other's stories, to acknowledge, with empathy, the other person's hurt or alienation, and to let go of anger. "Mending a conflict requires work on both sides," Petiford adds. "Deciding that the relationship is a priority and communicating your desire to work things out can be a good start to healing rifts."

This article originally appeared on USA TODAY: Prince Harry, Prince William and sibling rivalry: When brothers feud