Cole posted a series of photos with Frankie Lons Thursday with a lengthy caption to honor her late mother. She opens with, "This is so hard man. Can’t really even find the words. SMH. I honestly don’t even know how to feel. You can never prepare for something like this... Ever!!! but you will be missed."

While Keisha and Frankie weren't close while the singer was growing up -- she was raised by friends and relatives -- the two connected later in life, and their relationship was profiled on "Keyshia Cole: My New Life."

In Keisha's tribute to Frankie, she says, "I created this post to show my love and appreciation for your life and I would like to thank my fans + supporters, shooot your supporters and fans, for being here with us during these hard times, and the love that you all have for us.....the love for all your children was definitely felt."

It appears the family is organizing to have a service for Frankie in the near future with all of her kids in attendance, Keisha says, "When u said all you want is to have ALL OF YOUR CHILDREN IN ONE PLACE, AT ONE TIME meant the most to you, And I’m completely down to do that for you."

TMZ broke the story ... Frankie died at home in Oakland on Sunday, her birthday. Her son, Sam, told us she died of an overdose after a decades-long struggle with addiction.