The 'Twilight Saga' star is believed to have recently got engaged to the singer, whose real name is Tahliah Barnett, and the pair intend to marry this summer, with a low-key, relaxed celebration in London.
A source told the new issue of Grazia magazine: ''Tahliah wants to get married sooner rather than later and have what she's calling a 'bangers and mash' wedding.''
"She'd like a low-key registry office ceremony, pub lunch and party with their friends. They're talking about August.''
And the 27-year-old singer, who is known for her eccentric fashion sense, also plans to shun a traditional white gown for her big day.
The source added ''Tahliah doesn't intend to wear white. She wants this to be fun and a bid different.''
''It was recently claimed Robert is considering inviting his ex-girlfriend Kristen Stewart to his wedding.The duo split in 2013, just eight months after Kristen admitted to cheating with 'Snow White and the Huntsman' director Rupert Sanders"
However, a source said: ''Robert has been giving serious thought into inviting Kristen to his wedding.''
"They shared so much of their lives together, and both came to huge prominence at the same time with one another thanks to the 'Twilight' movies, so they'll always have something in common.''