The 31-year-old R&B singer, who has been accused of being a bad influence on Whitney, was seated next to the Bodyguard star's sister-in-law and former manager Patricia Houston and her daughter Bobbi Kristina.
Minutes before the tribute to Whitney, Patricia reportedly asked her security to remove Ray J - but he refused to leave.
According to TMZ, security warned Patricia that things were likely to get physical and it would almost certainly be caught on camera, so she grudgingly gave up.
Whitney and Ray J dated on/off for several years and even spent time together days before her death on February 11.
Following his row with Whitney's family, Ray J is said to have told friends yesterday: "Pat ruined what was a great opportunity to honour the woman who I loved."
Watch the Billboard Music Awards tribute to Whitney Houston below: