Sri Lankan-born newsreader George Alagiah has been diagnosed with bowel cancer, the BBC said today.
The corporation said that Mr Alagiah will be off-air for the near future while he receives treatment, adding that he is "optimistic" about the outcome.
The 58 year-old has been a familiar figure on TV news bulletins for many years.
The Sri Lanka-born journalist has been the face of BBC1's News At Six since 2007.
He has also been the main relief presenter of the News at Ten since 2000.
In a statement, the BBC said: "He is grateful for all the good wishes he has received thus far and is optimistic for a positive outcome.
"George asks that he and his family are given the space and privacy they require whilst he recovers.
"Our thoughts are with him and his family and we send them our very best wishes during this time.
"Until such time as George is well enough to return to work the BBC News at Six and GMT on BBC World News will be presented as usual by familiar faces from BBC News."
During his career, Mr Alagiah has specialised in Africa and the developing world, interviewing Nelson Mandel, Desmond Tutu and Robert Mugabe.
In 2004, he visited his grandfather's home in Sri Lanka in the aftermath of the Asian tsunami.