Cardwell passed away Saturday night due to complications from her stage 4 adrenal carcinoma, which had previously been described as terminal. Mama June broke the sad news online, writing ... "With the breaking heart, we are announcing that @annamarie35 is no longer with us. She passed away in my home last night peacefully at 11:12 PM."

MJ adds, "She gave one hell of a fight for 10 months she passed away with her family around her like she won’t and we will will be updating y’all with more information as we get it today. We love y’all and continued prayers and thoughts for our family doing this difficult time."

Cardwell's passing comes not long after her mother asked the public for prayers on Friday ... when she signaled Anna would be leaving this world soon.

June had told her followers in a video that the family was going through a transition, and that while Anna was still technically with them ... her life was in God's hands.

Anna had been diagnosed with cancer in January -- this after doctors did tests and found her lung, liver and kidney had been affected. She's said to have undergone chemotherapy in March, and was documenting her journey as recently as October on social media.

It sounds like things took a turn for the worse, though ... and Mama June's family is gutted.

Anna was a big part of their popularity in reality TV -- she'd appeared in several episodes of their hit shows "Here Comes Honey Boo Boo" and "Toddlers & Tiaras." She was very much so online, and had a fair amount of followers of her own ... upwards of nearly 250,000, in fact.

The last time we saw Anna was on the TMZ Tour, where she was riding like a normie and bantering with our camera person ... spitballing on what nickname she'd give Harvey Levin.

Anna is survived by her mother, June; her husband Eldridge, her two children, Kaitlyn and Kylee; and her three sisters: Lauryn, Alana and Jessica. She was only 29 years old.