Cardiff-born Nathan, 26, a centre and wing for the region has played for the Scarlets since February 2007 on a two-year contract.
Scarlets chief executive Stuart Gallacher said: "We're grateful to Nathan for his contribution to the squad since he joined us nearly two years ago. We wish him well in the future."
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland
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