11:07 AM PT -- Traci Braxton tells us, "LoLo was more than my niece, she was my daughter; and I, my son and husband are truly heartbroken over her passing."

10:45 AM PT -- According to the police report -- obtained by TMZ -- a friend of Lauren's claims she was talking with Lauren in the kitchen and went upstairs for just 10 minutes. The friend told cops when she returned to the kitchen, Lauren was on the floor and unresponsive.

8:22 AM PT -- Trina Braxton just posted about Lauren's death, saying, "God sent me another angel! Rest in Heaven Lauren "LoLo" Braxton."

Toni Braxton's niece has died in Maryland ... TMZ has learned.

Lauren Braxton -- the daughter of Toni's younger brother, Michael Conrad Braxton Jr. -- died Monday ... according to her father, who tells us her death was related to a heart condition.

Law enforcement tells TMZ ... they received a 911 call around noon on Monday, and Lauren -- who went by the nickname LoLo -- was unresponsive when they arrived. She was pronounced dead by paramedics.

Michael -- who is a Maryland native -- is the only son of the Braxton siblings. He and Toni are the elder siblings to Traci, Towanda, Trina and Tamar. Like most of his sisters, Michael is also a singer and songwriter and he's appeared on episodes of his sisters' reality show "Braxton Family Values."

Michael started singing with his sisters in church choirs when they were young.

His daughter Lauren was 24.

RIP