According to reports, things are going so well between the pair that Brandi, 43, invited 34-year-old Calum to spend Thanksgiving with her.
A source told Us Weekly: “They are sort of dating. It’s more of a hookup situation.”
Calum took to Instagram this week to share a snap of him with The Real Housewives of Beverly Hills star.
Alongside the photo, he wrote: “Filming with this lovely one [sic].”
Brandi also posted a photo of the pair of them enjoying the American holiday, and wrote: “Happy Thanksgiving everyone! [sic].”
In 2009 Brandi split from husband Eddie Cibrian, who she shares two children with.
During their marriage it was reported Eddie cheated on Brandi with country singer LeAnn Rimes – something he denied.
After splitting from Brandi, Eddie went public with LeAnn and their divorced was finalised in September 2010.
Calum split from girlfriend Ianthe Rose earlier this year.