Music legend Michael Jackson was 50 when he died from complications of a drug overdose in 2009, leaving behind his three young children. Prince, Paris and Blanket (who later changed his name to Bigi) moved in with their dad’s mother, Katherine Jackson, who became their legal guardian. As she raised the trio, she noted Prince was a “serious” boy who wanted to be a movie producer. “I see [Michael’s] talent in her,” she said of Paris, who excelled at art and music. Michael’s youngest, Katherine said, was “very playful, like Michael was.”

But Bigi’s not playing now. Nearly 15 years after losing his father, the 22-year-old is embroiled in a court battle with his 93-year-old grandmother, who wants Michael’s estate — which benefits the singer’s children — to pay a reported $500,000 in legal fees she’s racked up while challenging executors’ decision to sell half of the King of Pop’s $1.2 billion publishing and recorded masters catalog to Sony Music Group — a business decision Bigi, Paris, 26, and Prince, 27, have supported. “The family war has exploded,” a source exclusively tells In Touch. “Even though the selling of the catalog will benefit her grandchildren, Katherine continues to fight it. It’s sad because at one time the kids had a very loving relationship with their grandmother, but now there’s so much animosity.”

How Did the Legal Battle Between Michael Jackson’s Kids and Mother Begin?

Bigi was initially on the Jackson family matriarch’s side when she questioned a decision made by the estate’s co-executors, John Branca and John McClain, to sell half of Michael’s catalog for a reported $600 million. But after a judge last year ruled that the deal could move ahead, Bigi, Paris and Prince accepted the court’s decision. Katherine, however, did not and filed an appeal. “She was always very protective of Michael, and now she’s protective over the things he left behind, especially his music,” explains the source.

In December, she filed motions asking the estate to pay for her legal bills. In March, Bigi objected, stating in legal documents that it would be “unfair” to make him and his siblings fund a fight for Katherine, not them, chose to wage. “It is readily apparent that a reversal on appeal would be an extreme long shot,” Bigi’s lawyers wrote, explaining that “given those odds, Bigi decided not to waste his resources to participate in an appeal” that “is not for the benefit of the heirs.” Katherine hit back days later, claiming in court papers that the executors are being too frugal — Michael’s estate is worth a reported $2 billion — and the estate can afford to cover the fees she’s requested and still have “hundreds of millions of dollars available for the remainder beneficiaries.”

Tensions are high for the siblings and their grandma. “They don’t speak — they speak through their lawyers,” says the source, adding that the rift may never be healed. “It’s a shame, because Michael never would have wanted this.”