Kaia Gerber Shares Post About Grief After Brother Presley's Death

Kaia Gerber is sharing a heartfelt message about coping with grief after her brother Presley's death at 27.

Taking to Instagram ... she shared a stack of various books and novels that dealt with the topic of grief before picking out a particularly poignant quote by Joan Didion.

Kaia shared ... "Grief, when it comes, is nothing we expect it to be. Grief has no distance. Grief comes in waves, paroxysms, sudden apprehensions that weaken the knees and blind the eyes and obliterate darkness."

Just three weeks ago ... Kaia spoke out about Presley's death, sharing a lengthy letter addressed to him with her Instagram followers.

Kaia admitted she was "quite literally, down on my f***ing knees" ... and said she was "born loving you" and would "die loving you."

As you know ... Presley was discovered unresponsive in his room at Santa Monica rehab facility on Sept. 20. He had just checked into the facility hours prior.

While police investigate his death as a suspected overdose, his official cause of death is still pending.