The release of Mamma Mia! Here We Go Again marks quite a few milestones for returning star Meryl Streep. Not only is it the first time the three-time Oscar winner has appeared in a sequel to one of her films, it's also the first time she's reunited on screen with former Silkwood co-star Cher.
ET's Brooke Anderson caught up with the beloved screen legend on the red carpet at the London premiere of the musical comedy at the Hammersmith Apollo on Monday, and Streep dished on what it was like working with the iconic performer.
"It was fantastic," the 69-year-old actress marveled. "I came on the set the day that she sang 'Fernando.' That was my first day... And she just lifted the lid off the place! I mean, she steals the movie!"
Streep laughingly explained that Cher "appropriately" plays her mother in the long-awaited sequel -- which is once again based on the classic hit songs by Swedish pop group ABBA.
"Because she's lived a much longer life than I have," she added, jokingly referring to the fact that Cher is 72, only three years older than Streep herself.
The pair previously starred together in the 1983 drama Silkwood, based on the life of whistleblower and union activist Karen Silkwood, who died in a mysterious car accident.
ET caught up with Cher a day ahead of Monday's premiere, and the celebrated performer showered her co-star and long-time pal with effusive praise.
"We've stayed friends all these years. I cannot believe that, but [Silkwood] was my first film, and she helped me," Cher recalled. "I mean, she was unbelievable, because I had no idea what I was doing."
"It's great to see her [again]," Cher added, of working alongside Streep once more.
Their close friendship was radiant at the London premiere, where the actresses smiled broadly for photographers, and even shared a sweet kiss on the red carpet.
In both Mamma Mia movies, Streep also stars opposite Stellan Skarsgård, who plays one of her character's past lovers and possible fathers to her daughter -- played by Amanda Seyfried.
Coincidentally, in her role on the upcoming second season of HBO's hit drama Big Little Lies, Streep is set to play the mother of Alexander Skarsgård, Stellan's son.
While chatting with ET on Monday, Streep explained that she'd just been shooting scenes for the upcoming season a few days before having to fly to London for the premiere, and gushed over the experience of working alongside superstars like Reese Witherspoon and Nicole Kidman, who are also executive producers on the hit series.
"I love having the girls as my boss because they understand," Streep shared. "Like we have lots of big, fabulous, drunken meals together." Season two of Big Little Lies is expected to premiere in early 2019.
Mamma Mia! Here We Go Againhits theaters July 20.
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