According to one of Brickz's close friends, the pair met in 2016 in Diepkloof, Soweto and one thing led to another.
"They really don't care about what people think about their relationship. They are really trying to get through the next 15 years of their lives together," said the source. "She has been his support during this down-and-out phase of his life."
They send occasional letters back and forth and also do weekly visits.
According to the friend, she visits him in prison almost every Sunday.
Cas, who uses "Cazo" as her stage name, was born in Riverlea, west of Joburg. She is 35. She confirmed that she is dating the disgraced kwaito star but declined to comment further.
"Regarding my relationship with Sipho, I prefer not to comment on it," said the former Miss Riverlea pageant queen.
She also said she has been keeping busy with her modelling and music career. "What makes me different is the fact that I fuse 90s hip-hop with the modern sound."
Brickz was sentenced to 15 years in prison for raping his niece in 2013.
He could not be reached for comment.