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.
After spotting Cher arrive at the premiere, fans tweeted their praise. "I think it's always like, 'I'm so in love, so that person must be so in love with her, too.' I assume everyone's in love with Tommy because I'm in love with him".
The pair previously worked together on the 1983 drama Silkwood and, although this is the first time since then that they have starred alongside one another, Cher felt more relaxed knowing that she'd have the actress on hand to help her.
Cher said that her creative spirit was rekindled after singing one of the signature tunes on "Mamma Mia!".
I had a dream that writer-director Ol Parker's sequel to the feel-great Abba jukebox musical Mamma Mia! would recapture the giddy abandon of the first film, which smashed box office records in the summer of 2008 and had me dancing with fellow audience members at my local multiplex. "I can not believe that, but [Silkwood] was my first film, and she helped me", Cher recalled.
The addition of Cher as Streep's impeccably coiffed mother is a masterstroke. "I mean, she steals the movie!"
Cher also joins the cast, playing the mother of Streep's character Donna Sheridan, while James plays a younger version of Donna.
"After I did "Fernando" I thought it would really be fun to do an album of ABBA songs", the legendary pop icon told Kathie Lee Gifford on the Today show.