Former Wales Under-20 international Fawcett has joined up with his new team-mates ahead of the Guinness PRO14 fixture with Munster this weekend.
Haverfordwest-born Fawcett made his Scarlets debut in the Anglo-Welsh Cup, having worked his way through the Academy system at the region.
The dynamic 22-year-old, who is strong in the set piece and mobile around the pitch, represented Wales Under-20s during the 2016 Six Nations as they claimed the Grand Slam.
Head Coach Ceri Jones said: “Rhys has joined us on a short-term deal and boosts our front row resources, particularly with the likes of Ryan Bevington and Aaron Jarvis currently ruled out.
“Rhys is a talented young front row who is eager to make an impression in senior rugby, after impressing for Wales Under-20s and in the Academy system.
“We are pleased to have him join us and look forward to seeing Rhys make an impression in our set-up.”
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