Founder of alternative medicine group Universal Medicine, Serge Benhayon, will inherit the majority of a million-dollar estate following the death of one of his students despite her children's protests.
Judith McIntyre died aged 66 in June 2014 after a battle with breast cancer.
She left in her will $250,000 each for her children Seth, 41, and Sarah, 34, with the rest of her $1.1 million estate to go to Mr Benhayon.
A month before her death, Ms McIntyre also donated $800,000 to Mr Benhayon to renovate a warehouse on his Wollongbar property into a teaching hall.
She met Mr Benhayon at the Byron Bay Writers Festival in August 2011, about two months after she was diagnosed with breast cancer.
She soon became an adherent to his teachings.
In their supreme court challenge to the will, Seth and Sarah each claimed they needed $550,000 for home deposits and living expenses.
Seth said his mother had a history of giving large sums of money to spiritual gurus, including one to whom she donated $3000 a month and helped buy an apartment after becoming involved with her in 2002.
He said he urged his mother to reconsider bequeathing the majority of her estate to Universal Medicine.
"I encouraged her to pay in proportion to the services received; even generously, but with rationality," Seth said.
"I reiterated that spirituality, in my opinion, should not rest on money."
Sarah told the court she had agreed not to challenge her mother's will before her death because she "didn't want to upset her or to argue with her".
The court heard the Wollongbar teaching hall to which Ms McIntyre donated $800,000 was kept under Mr Benhayon's name, and he could legally sell it for personal profit.
But Mr Benhayon said: "My intention is to hold it and then pass it on to a company that will be able to own it for hundreds and hundreds of years".
NSW Supreme Court Justice James Stevenson said he had no reason to doubt Mr Benhayon's truthfulness.
"The strong impression I have from the evidence is that the deceased knew exactly what she was doing when she made her will," he said.
"She appears to have weighed up the competing considerations of the need to leave a legacy to Sarah and Seth and her desire to promote the teachings of Mr Benhayon."
The matter will return before the court for a decision to be made on costs.