A new witness in the Diddy criminal case says he has a manuscript belonging to Diddy’s late girlfriend, Kim Porter … but her best friend tells us Kim never tried to write a book.

Lawanda Lane, Kim’s best friend and the caregiver of Kim and Diddy’s twin daughters, tells TMZ … she was best friends with Kim for 30 years, including 20 years living under the same roof, and there was never a manuscript written by Kim.

Kim’s BFF tells us she was with Kim every day and Kim never wrote anything down … and she says the family doesn’t know who new Diddy witness Courtney Burgess is, even though the guy claims he’s one of Kim’s former associates.

As we reported … Courtney testified before a New York grand jury last week … and he also claims he has sex tapes showing celebrities getting down at Diddy parties.

There was a purported Kim Porter memoir on Amazon earlier this year, but it was pulled after her daughters denounced it and cast doubt on its authenticity … but now Courtney claims he has her manuscript.

Kim’s bestie says the guy is mistaken though … she says she was in charge of going through Kim’s belongings and distributing them to family and friends after Kim died, and if anyone would have found a manuscript it would have been her … and there wasn’t one.

But, Courtney’s lawyer, Ariel Mitchell, tells TMZ … he obtained the manuscript on a flash drive and it’s since been turned over to federal investigators in the Diddy case.