Since making a try-scoring debut for the Scarlets against Worcester Warriors in August 2005, the once-capped All Black has become a firm favourite with the fans. He has made 81 appearances for the Scarlets and scored 26 tries in the process.
A delighted Scarlets Chief Executive Stuart Gallacher said: "I am aware of the speculation surrounding the future of Regan and I am delighted to say he has committed his future to the Scarlets by signing a contract for three years."
King's contract will keep him with Phil Davies's side until July 2011.
"Regan is a very integral part of the squad and is a world class performer and his signature shows how determined we are to build for the future," added Mr Gallacher.
The 27-year-old King said: "I've enjoyed my time at the Scarlets and with a new state of the art stadium to play in just around the corner, I wanted to be part of what I am sure is going to be a successful future for the region."
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