Us reports that Heyward, 30, died on Saturday, and no cause of death has been announced by the L.A. County Coroner's office yet.
Odom, Heyward and Sangouthai were reportedly all friends. Sangouthai died on June 14 -- allegedly from a drug overdose. Heyward's most recent Instagram post was actually a tribute to his late friend.
"#RIP To my big brother Jamie who always brought light into any room he walked into and laughter as well at all times," Heyward wrote in the caption. "J you will always be missed. Family for life. #BandOfBrothers."