Stefan joined the Ospreys during the first season of regionalised rugby in December 2003 after earning 37 South African caps. He will have played 87 times for the Ospreys by the time he returns home on Saturday.
Terblanche said: "There have been so many highlights during my four years at the Ospreys. When I joined the region the Ospreys were just a name, a vision and a group of players.
"The organisation has now grown into one of the most professional outfits in world rugby with two Magners League titles, an EDF Energy Cup Final and beating the Aussies at the Liberty Stadium being the obvious highlights during my time at the region. There are so many other memories of my time in Wales that I will take back to South Africa but I will particularly remember the supporters and their passion for rugby in the region.
"The Ospreys have a large and growing fan base, a young talented squad of players, excellent facilities and a fantastic Stadium at the Liberty and I can only see the region going from strength to strength over the next few years. I am sure that the next four years will be even more successful than the last four."
Head Coach Lyn Jones added: "Stefan is a true gent and he will be missed both on and off the field. During his time at the Ospreys he has shown his quality as an international rugby player and he has been great ambassador for South Africa.
"Whilst he is contracted with us through to the end of this season we respect his wish to return to South Africa to fulfill his unfinished ambitions with the Natal Sharks."