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Tennyson had a child with Simmons, 2-year-old Sutton Joseph Tennyson.
Simmons is the daughter of Rev. Run, one of the founding members of legendary hip-hop group Run–DMC.
The victim was found dead with multiple gunshot wounds inside the open garage, APD spokesman Officer Jarius Daugherty said in a statement.
Police said a preliminary investigation suggests that Tennyson was talking in the driveway with another man when “the conversation escalated” and the man shot Tennyson multiple times.
The man left the scene in a car, and the shooting is under investigation.
Simmons, whose career includes appearing on several reality television shows, made an Instagram post about her ex-fiancé on Sunday, including pictures of him with their child.
“Thank you for leaving behind my greatest gift,” she wrote. “I’m hurting. I’m numb.”
Simmons also posted a video of Sutton Joseph watching a video of Tennyson playing with him in a pool. Simmons is heard on the video saying, “Peek-a-boo!” as Tennyson laughs, dipping their son in the water.