South Africa's Supreme Court has rejected an appeal by former Grand Slam tennis champion Bob Hewitt, ruling that he must serve a six-year jail sentence after being convicted of the rape and sexual assault of young girls he coached decades ago.

A panel of three judges at the Supreme Court of Appeal said in a judgment released Thursday that the prison sentence given to Hewitt was appropriate. Hewitt, now 76, was convicted of the offenses last year.

He was found guilty of raping two girls and sexually assaulting a third in the 1980s and 1990s.

The Australia-born Hewitt won 15 Grand Slam titles in doubles and mixed doubles.

He has been held under a form of house arrest at his farm in southern South Africa since his conviction.