Thomas arrived at the base at Crystal Springs for the altitude camp on Monday, and is set to spend two weeks training with his three-time Tour de France winning teammate Froome.
In 2015 Wout Poels joined Froome, who spent some of his childhood in South Africa.
Last year Boswell spent time with Froome in South Africa, where the latter created a secret Strava account under the guise of 'Luke Skywalker' before swiftly deleting it after he was uncovered. Now, Thomas is working with Froome ahead of his debut tilt at a Grand Tour title at the Giro d'Italia in May.
Information gleaned by Cyclingnews (opens in new tab) suggests coach at Team Sky Tim Kerrison as well as mechanic Gary Blem and soigneur Jacek Walczak have also joined the British pair in South Africa, after they both made their season debuts in Australia.
Thomas rode the WorldTour Tour Down Under, while Froome returned to the Herald Sun Tour which he won in 2015.
Froome also completed a training block alongside new French recruit Kenny Elissonde while Down Under, with Elissonde saying training alongside Froome was harder than riding the Tour Down Under.
While Froome is almost certain to begin his European season at the Volta a Catalunya in March with the Tour de France his long-term target, it's unclear how Thomas's race programme might be altered with the Giro in mind.
Last year the Welshman won Paris-Nice before heading to Milan-San Remo and then Catalunya. Mikel Landa, who led Sky last year at the Giro and will lead alongside Thomas this year, raced the Tour of the Basque County and the Giro del Trentino in preparation for the Grand Tour, suggesting Thomas could be in for a change this year.
Tirreno-Adriatico is a traditional starting point for Giro contenders, so could be where Thomas heads after the South Africa camp.
What is certain for Thomas however is that he won't face any of the Classics. Despite a focus on stage racing in the past few years, Thomas still raced the Tour of Flanders last year, a race he says he's always dreamed of winning.
Many other riders have taken to using South Africa as a location for training in the early season. Orica-Scott have for a few years taken riders for altitude training there, while Team Sunweb duo Tom Dumoulin and Michael Matthews are there already preparing ahead of their first races of 2017.
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