(CBS News) The fight over the estate of popular artist Thomas Kinkade is going to court.
His mistress says she has two handwritten notes, proving she should be due millions.
A hearing on July 2 will determine whether those notes were actually written by Kinkade, who died in April at age 54.
Kinkade painted for the masses, becoming the most commercially successful painter in the world. His paintings came off the presses like money, earning Kinkade an estimated $100 million a year before his death. His pastoral style holds the key, as he told "60 Minutes" back in 2002:
"Everyone can identify with a fragrant garden, with the beauty of sunset, with the quiet of nature, with a warm and cozy cottage," he said.
But it's the authenticity of the handwriting on letters that could decide who controls large portions of the late painter's mansion and fortune.
Amy Pinto-Walsh, Kinkade's girlfriend at the time of his death, went to court this week with two letters she claims Kinkade wrote before his death.
They allegedly leave her $10 million to establish a museum of Kinkade's original paintings; his mansion; and legal authority over $66 million from his estate.
Kinkade's estranged wife Nanette said she is the sole executor of his will and trust, and calls Pinto-Walsh a golddigger.
Journalist Julia Prodis Sulek, who's been covering this case for the San Jose Mercury News, told "CBS This Morning: Saturday" that because the matter will be handled in arbitration rather than in open court, some very sensitive issues will be decided behind closed doors - one issue being the medical directive.
The mistress, Sulek said, claims that the estate violated that: "She said that Thomas had given her - when he was sick in the hospital - medical directive over his medical issues as well as the disposition of his body should he die. The morning of his death, she said she wasn't given that authority, that people close to his family came in and took care of the body and, worse yet, banned her from the funeral. So that's one issue.
"The other is that the estate said she violated a confidentiality agreement. So she can't say anything and they say that if she were to talk, they fear that she would say horrible things that would defame him."
Celebrity divorce lawyer Raoul Felder said the letters on which Pinto-Walsh is basing her claims are "worthless."
"They've got to be in writing, they've got to be notarized, so none of this stuff is worth anything legally here, because it doesn't adhere to the statute of wills," Felder said. "It makes nice talk," he offered.
But Felder added that Kinkade's family made a mistake by bringing the matter to arbitration rather than a court. "The reason why the estate wants it confidential is because there's four daughters here and there may be a lot of garbage. But they made a tactical mistake, because they would be better off in court. In court the judge would throw it out. ... In arbitration, they're more lenient - people sit around the table and they're more friendly and may work out a settlement to the girlfriend."
To watch the interviews with Felder and Sulek click on the video player above.