Saracens have released prop Deon Carstens to enable the South African to join Western Province in his home city of Cape Town.
The 32-year-old has made 29 appearances for the Premiership side since joining from Sharks in July 2010, 10 of which came this season.
He has nine Springbok caps, the most recent coming two years ago.
"I am very sad to be leaving Saracens. But I am massively looking forward to the opportunity in Cape Town," he said.
"I am also very grateful to Saracens for their pragmatic approach to this situation.
"This is a special club. It's run in a different way to any other rugby club in my experience, and it is undoubtedly the right way."
Director of rugby Mark McCall added: "We have a partnership with Western Province rugby, and any partnership must work both ways.
"The Stormers urgently need a top class international loose-head prop for the forthcoming Super Rugby season, the move makes sense for the player and so we have agreed to the release."
Meanwhile, Saracens have announced their Heineken Cup match against Biarritz next year will be held at the Cape Town Stadium.
Chairman Nigel Wray said: "It makes perfect sense for us to play a home game in South Africa, as we work hard to expand our commercial and supporter base."