He joined the Golden Lions for the 2013 season,[4] but was seriously injured in a car crash shortly after joining, which ruled him out until at least the end of 2013.[5] He fully recovered and was included in the Lions squad for the 2014 Super Rugby season[6] and made his debut in a 21–20 victory over the Cheetahs in Bloemfontein.[7][8]
Mostert was named in South Africa's squad for the 2019 Rugby World Cup.[10] South Africa went on to win the tournament, defeating England in the final.[11]
It was confirmed he had left Gloucester in June 2020 in order to pursue a career in Japan.[12] It was later confirmed that Mostert returned to Japan Top League competition to sign for Honda Heat for their next season.[13]
Notes
^ French Top 14 side Lyon also announced that they signed Mostert from 1 November 2016 onwards (or after the November internationals if he is involved). However, the Ricoh Black Rams then announced that they signed Mostert on a two-year contract, and South African media reported that he will return for the Lions in 2017. In October 2016, with Mostert joining Ricoh Black Rams, Lyon threatened to take legal action against Mostert.[3]