Brand's "RustyRocket" handle is no longer included on Katy's list of 83 people she follows.
Russell, however, is still following his estranged wife on his Twitter page.
The couple had a flirty history on Twitter, which included Russell infamously posting a picture of his wife with no make-up.
A source told Us Weekly: "She's limiting those interactions. He's being so atrocious that she feels like she never really knew him. She doesn't want to look battered and have people for sorry for her. She's very strong and confident. Katy is insulted and feels betrayed that Russell has treated her so poorly. She will never forgive him. Ever."