Pollyanna and The Parent Trap star Hayley Mills brought in big bucks for Disney when she was just a teen.

Mills grew up in the entertainment industry in the U.K.—her mother, Mary Hayley Bell, was an actor and playwright, and her father, Sir John Mills, was a star in Britain. He co-starred with his daughter in her debut feature, Tiger Bay, in 1959. That movie led her to ink a deal with Disney, which included the lead role in Pollyanna a year later and then The Parent Trap in 1961.

The Parent Trap was one of the most successful films of that year, grossing $25.1 million at the box office. Mills soon received an honorary Juvenile Academy Award, an honor that had previously been given to child luminaries including Judy Garland and Mickey Rooney.

Mills' film career flourished at Disney over the next six years, and her star continued to rise, but her roles were limited to safe ingenue parts, and she eventually left the studio to take more mature parts.

RELATED: A Former Child Star Just Explained How She "Blew All Her Disney Money."

Mills later learned that the money she'd made as a Disney star had been heavily taxed and she was out millions.

Mills expected a big payday from her run as a child star. The money she'd made from her Disney movies had been put in a trust that she was told she could access when she turned 21. But Mills was in for a shock when she went to retrieve her paycheck.

The money, she discovered, had been heavily taxed by the British Revenue Service, at an astonishing rate of 91 percent. She described the moment she found out most of her money was gone in an excerpt from Forever Young in The Daily Mail. "Well, my dear, basically, the Revenue have attacked your trust company," her lawyer Stanley Passmore told her. "They're going to tax you at the full rate: 91 percent of the entire trust."

"I felt the blood drain from my face," she recalled. Then, the lawyer told her with a laugh: "Nothing you can do, really. You could contest it but if I were you, I'd leave the country! ... You should have repudiated the trust before you reached 21, but I'm afraid it's too late for that now."

Mills took the fight for her money to court.

Mills was later told the high tax rate was meant to help the Inland Revenue Service rebuild England after World War II. She was advised to sue either her lawyer or her father over the lack of proper advisement on the fund, but she chose neither.

Instead, she submitted a tax appeal. After waiting two years, a judgment was ruled against her. She appealed the ruling three years later and lost again in 1971.

Finally, in Oct. 1972, she wrote in Forever Young, "my tax case went up before the Master of the Rolls, Lord Denning. Pointing out that I'd already paid tax on my earnings and shouldn't have to pay a surtax, he ruled that the money belonged to me," she wrote.

Ultimately, Mills lost about $17 million.

Mills celebrated momentarily, but the House of Lords appealed Denning's ruling in 1974 and shot it down for good. Mills says she ultimately lost around £2 million, the equivalent of $17 million today. "The state had plundered my trust like a horde of pirates," she wrote. "The Disney money was all gone."

"I never saw it,” Mills told the Los Angeles Timesin a new interview. “I knew it was there and one day I would have it, but it was just sort of a dream, and then one day the dream was gone. Occasionally, I think: It would have been nice if I had the freedom to say no."

Of the loss, Mills was resolute. "Of course, I mourned the loss of the freedom my small fortune might have given me—but not the money itself," she wrote in Forever Young.

“The way she describes the experience of having all that money taken away is very innocent—like, how can you feel sad for something you never had,” her son, Crispian Mills, who helped with the book, told the L.A. Times. “And I think people will now realize that there is an element of Pollyanna in her that is very real. That was truth coming across on screen.”

RELATED: 17 Former Child Stars Who Have Totally Different Jobs Now.