Herbst, who is on contract with the Vodacom Bulls until the end of October, was loaned to the Kings earlier this season after it seemed he would not get regular game time behind Lood de Jager, RG Snyman and Jason Jenkins at the union.
And the big bearded lock has made the most of his chance at the Kings, playing a vital role in the pack and being one of the standout players in the revival of the franchise under coach Deon Davids.
Herbst will return to the Blue Bulls for the Currie Cup season and is likely to see out his contract there, and then make the move to Italy at the end of the current South African season as the Bulls are likely to need his services with De Jager set to be called up for the Springboks and Snyman heading to Japan for the Currie Cup part of the season.
