Britney made the big announcement Friday morning that the audio version of "The Woman in Me" will be recorded by Michelle. Britney herself did record the prologue to her memoir, but Michelle did the rest.

Brit told People, "Reliving everything has been exciting, heart-wrenching, and emotional, to say the least. For those reasons, I will only be reading a small part of my audiobook."

TMZ broke the story ... Britney just found it too painful to record several chapters of the book -- particularly those dealing with her family members, from whom she's currently estranged. They had attempted to get Reese Witherspoon on board, but couldn't work out the scheduling.

Britney says she's grateful to Michelle for doing the heavy lifting in the recording booth.

Michelle, who's last Oscar nom came for last year's "Fabelmans," has never voiced an audiobook before, but clearly wanted to support the pop star.