Mitt Romney Sister-in-Law's Cause of Death Released

Mitt Romney's sister-in-law's cause of death has been released -- she died by suicide, TMZ has learned.

The L.A. County Medical Examiner determined 64-year-old Carrie Elizabeth Romney died from blunt traumatic injuries after falling from the rooftop of a parking structure in Valencia, California, north of Los Angeles, back in October.

Carrie was in the midst of a divorce when she tragically died -- her husband, Scott, had filed back in June, citing "irreconcilable differences."

They tied the knot back in 2016 -- and Carrie was Scott's third wife.

Following Carrie's death, Romney told the Daily Mail ... "Our family is heartbroken by the loss of Carrie, who brought warmth and love to all our lives. We ask for privacy during this difficult time."