Sources connected to the investigation tell TMZ ... MB's mom, Leslie Joanne Wayne, appears to have been murdered by her spouse -- not Metro's father -- who then killed himself. We're told this happened Friday night, but further details are hazy.
An autopsy will be conducted for an official cause of death. Metro's rep confirms Leslie died this weekend -- adding that he and his family request privacy during this difficult time.
Leslie raised Boomin and his 3 siblings in St. Louis. Word is, she was one of the first people to notice her son's musical talents ... and encouraged him to pursue his passion through adolescence and early adulthood. She'd even drive him from STL to Atlanta so he could collaborate with artists he was connecting with, all in hopes of getting his career started.
She and her boy were incredibly close -- even when Metro achieved international stardom, she was always at the forefront of his mind.