The REM frontman said that Cobain was on the verge of achieving something "phenomenal" before he killed himself in 1994.
Stipe told DeathandTaxes: "He had reached a point where he was about to push through to something that was so phenomenal and so beautiful.
"It was all written, it was all right there and it was so obvious where he was going, and then he didn’t make it.
"I still have trouble - I can’t listen to an entire Nirvana record."
REM's track 'Let Me In', from their 1994 LP Monster, was allegedly written for Cobain shortly after his death.