South Africa's first black president Nelson Mandela invited one of his former jailers to help mark the 20th anniversary of his release from prison at a special dinner.

The Nobel Peace Prize winner spent 27 years in prison under white-minority apartheid rule, mainly on the notorious Robben Island near Cape Town. His release on February 11, 1990, set South Africa on the path to democracy.

Christo Brand was a Robben Island warder, but the two developed a friendship that Mandela said in his memoirs had "reinforced my belief in the essential humanity of even those who had kept me behind bars."

Brand was among a small group invited to Mandela's home late Wednesday for a dinner with his ex-wife Winnie Madikizela-Mandela, his daughter Zindzi, and leading anti-apartheid activists.

At the party Brand asked Mandela, a boxer in his youth, if he still exercised, according to the Sapa news agency.

"It's not easy, but I do it every now and then. I do feel like I am getting old. Time is flying. I'm not really worried," 91-year-old Mandela said.

Zindzi Mandela filmed the event for a documentary called "Conversations About That Day", which she plans to screen for the anniversary next week.