Grandjean was also selected as a reserve for the Belgian squad at the 2012 Summer Olympics in London, but did not compete in the 4 × 200 m freestyle relay. His teammates Louis Croenen, Dieter Dekoninck, Pieter Timmers, and Glenn Surgeloose failed to reach the top 8 final, finishing only in twelfth place with a time of 7:14.44.