By July 1964, John Lennon and the Beatles had triggered Beatlemania in the UK and taken America by storm by performing on “The Ed Sullivan Show” and landing 12 singles in the Billboard Hot 100 chart.

Meanwhile, troubled Hollywood star Judy Garland was in a fragile mental and physical state — and fewer than five years years away from her death.

Lennon and Garland, two icons of 20th century popular culture, crossed paths in a now famous concert at London’s Palladium Theatre on July 23, 1964.

Twenty-four-year-old Lennon, leading the so-called Youthquake, and 42-year-old Garland, representing the outdated Hollywood studio system, were among the entertainers at the Palladium to perform for the annual “Night of the 100 Stars” charity benefit. Queen Elizabeth II was in the audience, and Laurence Olivier was another star on the bill.

Also on the bill that momentous night was Disney child star Hayley Mills, as she recounts in an interview last week on film critic Leonard Maltin’s Maltin on Movies podcast.

Mills said she met the Beatles for the first time that night backstage. She was 16. For their performance, the Beatles performed two songs and acted in a ballet sketch that had them being suspended high above the stage.

Mills said she would get to know all of the Fab Four a few years later when she went on a single date with George Harrison and when Paul McCartney scored the soundtrack for her first “grown-up” movie, the 1966 working class comedy drama “The Family Way.”

When asked who her favorite Beatles was, Mills, who also starred in “Pollyanna” and the original “Parent Trap,” said, “It’s so hard to choose.”

“They’re all so wonderful and brilliant and unique,” she said. “I adored all of them, but I was a little bit in awe of John. He was so smart and you never knew what he was going to say next.”

Meanwhile, Starr was “great fun, really fun,’’ she said before getting around to Harrison. She admits she still has a soft spot for him, “an extremely soft spot. I went out with George, but only once, only once.”

That night at the Palladium, Mills said she also she got a taste of the way you could never predict what the famously wry, sometimes cruel Lennon would say next.

For example, that night Lennon said to the crowd: “Those in the cheap seats clap, those in the expensive seats rattle your jewelry.”

But then Garland became the target of one of his quips, and his comment was definitely on the cruel side, as Mills explained.

Numerous biographies point to the fact that Garland struggled for much of her life with addiction to alcohol and various prescription medications and was prone to debilitating bouts of depression. In 1959, she had been hospitalized for hepatitis and cirrhosis of the liver, which doctors predicted would permanently derail her career, the Daily Mail said. Moreover, she had attempted suicide multiple times.

One of those suicide attempts apparently occurred just before the Palladium concert. According to a 1964 United Press International account, Garland had gone “to hospital” in London for what she claimed were “accidental” cuts to her arms.

She said she had injured herself while using scissors to open a trunk bound with metal. From there she went to a nursing home, “because I needed a good rest.”

Three hours before showtime, Garland left the nursing home.

Mills said she arrived at the Palladium looking “wonderful.”

“She had just come out of hospital and was wearing a wonderful red sequened sheath dress with long sleeves,” Mills said. “There were sequins everywhere.”

At this point in her interview with Maltin, Mills wondered if she should go on but figures she’s come this far already. She continued, saying that she was in the wings with the Beatles when Garland walked on stage.

“There was tremendous applause and then there was a lull before she started to speak or or sing,” she said.

“And in that lull, you suddenly heard John’s voice, yelling out, ‘Show us your wrists, Judy!’”

Mills said, “There was an awful pause as you can imagine.” But Mills adds, “I don’t think she heard. I hope she didn’t hear.”

Mills reflected that Lennon’s bitterness probably stemmed from the fact that he had a hard life growing up. Lennon himself acknowledged in a 1980 Playboy interview that he had been violent and cruel to women, especially to his wives and to women he dated. The interview took place shortly before Lennon was shot and killed outside his Manhattan apartment in December 1980.

“I was a hitter. I couldn’t express myself and I hit. I fought men and I hit women,” he said. This violent history was why he worked to transform himself into someone who embraced peace, especially in his political activism, he said. “That is why I am always on about peace, you see. It is the most violent people who go for love and peace.”

If Garland heard what Lennon shouted to her that night, she didn’t let it affect her performance.

She essentially stole the show, inspiring the kind of excitement the Beatles typically generated on the “Ed Sullivan Show” an everywhere else.

The audience jumped to its feet for Garland, “cheering, stamping and shouting ‘sing, Judy, sing,’” according to UPI. They cried for her to deliver “Over the Rainbow.” Her performance brought down the house.

Then she gave the crowd an encore of “Swanee.”

The other entertainers, including the Beatles, “faded into the wings,” the UPI story said.