Nelson Mandela is currently being treated for a lung infection, which is basically pneumonia.
South African officials said that Mandela's infection is "recurring."
He is 94-years-old and at that age, it's very easy for fluid to build up in the lungs.
Because pneumonia doesn't always have traditional symptoms like fever and cough, it could have taken a very long time to diagnose in Mandela.
Pneumonia is very serious, especially in someone his age, but it is usually treatable.
We hope he gets better soon and recovers completely!
[Image via AP Images.]