The popular actress, who plays Donna, has been missing from the trailers and hasn’t played a big role in the movie’s publicity campaign.
As a result, fans have been busy speculating that Donna may have died since the events of the first movie, and will show up only in spiritual or flashback form.
Still, Streep beamed in a new featurette that the new film has “an incredible joy”.
“I really never thought that there would be a sequel,” she admitted.
“When this script came, it took my breath away.”
She added: “Walking onto the set and seeing Colin [Firth] and Stellan [Skarsgard] and Pierce [Brosnan] and Christine Baranski and Julie Walters and Dominic [Cooper] and Amanda [Seyfried]…
“The music starts up and you put on the spandex and honey, it all comes together.”
Of the finished product, she declared: “It just has an indescribably joy in it, and pure fun.”
The tracklisting for the sequel’s soundtrack has finally been revealed ahead of its release on CD and digital download tomorrow (July 13).
Streep will be performing My Love, My Life with Amanda Seyfried and Lily James, and The Day Before You Came as a solo number.
She is also credited as part of the ensemble in Super Trouper.
Cher has joined the cast to play her mother, and will sing Fernando; while Lily James plays Donna’s younger self.
James has the lion’s share of the music; singing on When I Kissed The Teacher, I Wonder (Departure), Waterloo, Why Did It Have To Be Me?, I Have A Dream, Andante Andante, The Name of the Game, Knowing Me Knowing You, Mamma Mia, My Love My Life and Super Trouper.
Mamma Mia: Here We Go Again! is out on July 20.