Former Paralympian Oscar Pistorius had had a jail sentence extended from six years to 13 years and five months for his role in the death of his girlfriend Reena Steenkamp, who was shot six times in their home in February 2013.
Prosecutors had argued that the initial six-year term for murdering Reeva Steenkamp was too short.
Pistorius claimed he shot dead Steenkamp on Valentine's Day after mistaking her for a burglar.
In 2016, a judge sentenced Pistorius to six years in prison for shooting Steenkamp through the bathroom door of his house in 2013.
Pistorius, the first amputee runner to compete in the Summer Olympics at the London 2012 Games, was banned by the International Paralympic Committee for five years in 2014 when his murder trial began.More news: Different alcoholic drinks cause different moods
Prosecutor Gerrie Nel argued that Pistorius' sentence was "shockingly lenient", while the defense sought to dismiss the appeal.
"They feel there has been justice for Reeva". The court agreed and the sentence is now 13 years.
Judge Masipa ruled that although the Steenkamps had suffered a great loss, Pistorius' life and career were also in ruins.
Big developments in South Africa this morning..
Pistorius' lawyers have just one avenue open to them if they want to challenge the new sentence handed down by the Supreme Court, and that is to appeal to the Constitutional Court, the highest court in South Africa.More news: Manchester United boss Jose Mourinho: 'Everyone to blame for Basel defeat'
"I did not expect the Supreme Court of Appeal to hand down such a lengthy sentence of imprisonment", legal analyst Ulrich Roux said on the eNCA news channel. Fifteen years is the country's usual minimum sentence for murder.
The athlete was originally convicted of manslaughter and sentenced to five years in jail.
This is the third time Pistorius has faced a different sentence in the case.
Pistorius failed with an appeal to the Constitutional Court previous year to challenge his murder conviction.More news: Glenn Maxwell added to the squad as cover for David Warner
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