Nelson Mandela's grandson is behind bars ... accused of raping a 15-year-old girl in a restaurant bathroom.
24-year-old Mbuso Mandela appeared in a Johannesburg court Monday and will remain in custody at least until another hearing on Friday.
A spokesman for the victim's family told the Daily Sun ... the incident happened on August 7, when Mandela followed the girl into the restroom and "grabbed her and raped her inside one of the toilets."
The Sun also reports the family claims Winnie Mandela sent her bodyguard to their home after the incident in an attempt to talk them out of pursuing the case.
Mbuso is one of Nelson Mandela's 17 grandchildren.