Hayley Mills skyrocketed to fame as a child star under Walt Disney’s wing for seven years — only to see her once-promising fortune slip away.

The actress, whose most memorable roles included "Pollyanna" and "The Parent Trap," recently appeared alongside her sister, Juliet Mills, on "The Rosebud Podcast." The appearance celebrated Mills’ 80th birthday.

When host Gyles Brandreth pressed Mills on what became of "the millions" she earned during her Disney years, she replied, "I gave it to the tax man."

FORMER DISNEY CHILD STAR WOKE UP TO 'ZERO DOLLARS' IN BANK ACCOUNT AFTER NEARLY 20 YEARS IN SHOWBIZ

"It was rather a big chunk," she admitted. "It was most of it because it was all put into a trust fund, because super tax was 90% in those days, so they had to do something."

"I do know the background of this, and it’s partly because you were poorly advised," said Brandreth. "But also, it was partly to do with the naïveté of your father, I think. There was an innocence about him and a sort of optimism."

"He had a business manager who made those sorts of decisions," Juliet, 84, chimed in.

WATCH: HAYLEY MILLS RECALLS PERSONAL BOND WITH WALT DISNEY ON SET

The Mills sisters come from a celebrated British acting family. Their father, Sir John Mills, was one of Britain’s most respected actors and had a career that spanned decades. Their mother, Mary Hayley Bell, was also an actress and a playwright.

"Stanley [Passmore] also advised Daddy, and not very well," said Mills, referring to the family’s solicitor. "The trust company was set up for me. Stanley was also involved in setting up a trust company for [actor] Jack Hawkins. And the Inland Revenue attacked his trust company, which affected British law. It created the precedent."

"And so, when I reached 21, instead of being given the key to the door, I was handed an envelope across a green baize tablecloth by Stanley, which was the Inland Revenue basically saying, ‘Thank you. You owe us 90% of your earnings,’" Mills continued. "And I’ve never been good at figures."

"I said, ‘Well, what does this mean? I don’t understand.’ And Stanley laughed and said, ‘Well, I think it means you have to move to America [for work].’ And that’s all he ever said. He was a crook. He didn’t give a flying Dutchman."

The Times of London reported that when Mills turned 21, she went to collect her money from the trust that her father and Passmore set up for her. However, she discovered that the trust hadn’t been set up correctly, and she had to pay a surtax of 91% on everything in it. While she contested it fiercely, there was no solution beyond suing her father or Passmore, the outlet reported.

On the podcast, Mills said she had a meeting with a prominent lawyer in hopes of fighting the case, but "it didn’t work."

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Lord Denning, one of Britain’s most powerful judges at the time, briefly gave Mills a win in her fight with the tax authorities. In the 1970s, he ruled in her favor, agreeing that it was unfair to tax her Disney earnings the way the government had. However, the victory didn’t stick. The case went to the House of Lords, which overturned Denning’s decision, leaving Mills on the hook for the massive bill that wiped out much of her fortune.

Mills pleaded her case to the British government for years, the Los Angeles Times reported. However, her appeal was denied for good in 1975. If she had won, Mills said she would have been able to keep about 2 million pounds, which is well over $17 million today.

Mills kept working.

"I didn’t have a sensible enough sense of my career and what I ought to be doing, but I didn’t want to do more Disney movies," said Mills. "I wanted to spread my wings and have a greater choice and not be limited by that.

"[But] I didn’t know what to look for. I didn’t know who I was. There was this moment when we’re growing up where we’re really on that uncomfortable seesaw, being still one foot in childhood and the other foot in being a woman. And I found it awfully difficult to get both feet into womanhood because [there] was a part of me that didn’t want to disappoint people. ‘Oh, she’s not that cute little girl anymore. She’s what?' I didn’t know what sort of thing to look for."

After she became a mother, Mills did some stage work and took on a handful of TV gigs in the U.S., the Los Angeles Times reported. She still acts occasionally.

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Back in 2021, Mills told Fox News Digital she was "fortunate" to have had a better outcome than many other child stars in Hollywood.

"I was working for a studio with a boss who was a genuinely good man," she explained at the time. "He cared about the people who worked for him. I also had the support of my parents, who were both in the business. So I had support. The business can really come at people like an express train. You’re suddenly surrounded by wealth and showered with attention at an immense pace. It’s very intense and very, very easy to lose your way unless you have that support."

"I certainly had my struggles," Mills admitted. "But I think we all face struggles growing up. You’re trying to make sense of life and who you are, except you’re trying to figure all of this out in Hollywood. When you’re in that environment, it’s hard to hang on to reality. But after I worked, I went home. I went to boarding school in England. So, in some ways, I think I had it better than others."

In a recently reshared 2017 interview with "Nostalgia Tonight with Joe Sibilia," Mills spoke of her close relationship with Disney, who died in 1966 at age 65.

"He was a great friend of my family as a result of my working there," she told the outlet. "He got on terribly well with my mother and father, particularly my mom, who was very funny and had a wicked sense of humor, which Walt really appreciated. So, I always felt very happy in his company. He was a very warm, kind and sweet man. I loved him. I was really fond of him."

"I always knew he was a brilliant, wonderful, amazing man," Mills shared. "And he took us around his fantastic Disneyland. He took us all around. And how amazing is that, to be taken around Disneyland by Walt Disney? But I didn’t appreciate at the time how lucky I was to have actually begun my career in that studio with him at the head of it, because he ran it so well, and it was small, and everyone knew everyone else, and everyone knew everyone’s name. And so did he."