Wellbrock qualified to represent Germany at the
2020 Summer Olympics, held in
Tokyo,
Japan and postponed to summer of 2021 due to the
COVID-19 pandemic.[6] His first medal of the Olympic Games was in the
1500 metre freestyle, where he won the bronze medal.[7] Wellbrock also won a gold medal in the
10 kilometre open water swim a few days later with a time of 1:48:33.7, which was over 25 seconds faster than the second-place finisher.[8] His gold medal was the first won in the event at an Olympic Games by a swimmer representing Germany.[7] His Olympic medals in pool swimming and open water swimming marked the second time a swimmer won medals in both disciplines at one Olympic Games and he was closely followed by the third swimmer to do so,
Gregorio Paltrinieri of
Italy who also won a medal in each discipline at the 2020 Summer Olympics only Gregorio Paltrinieri won his second medal, a bronze medal in the 10 kilometre open water swim, seconds after Welllbrock and thus Wellbrock became the second swimmer in history to achieve the feat and Gregorio Paltrinieri the third.[9]
2021 European Short Course Championships
At the
2021 European Short Course Swimming Championships, held at the
Palace of Water Sports in
Kazan,
Russia, Wellbrock won a gold medal in the 1500 metre freestyle on 4 November with a time of 14:09.88.[10] On 7 November, Wellbrock won the silver medal in the 800 metre freestyle in 7:27.99, finishing five-hundredths of a second behind gold medalist in the event Gregorio Paltrinieri.[11]
2021 World Short Course Championships
At the
Abu Dhabi Aquatics Festival, held in parallel with the
2021 World Short Course Championships, in December 2021, Wellbrock won a bronze medal as part of the open water 4×1500 metre mixed relay event.[12] In his individual event, the 10 kilometre open water swim, Wellbrock won the gold medal in a time of 1:48:09.4, finishing over two seconds ahead of silver medalist
Domenico Acerenza of
Italy.[13] As part of the World Championships, Wellbrock swam a 14:25.79 in the prelims heats of the
1500 metre freestyle on 20 December, qualifying for the final the following day ranking third.[14] In the final of the 1500 metre freestyle, Wellbrock set a new
world record with a time of 14:06.88 and won the gold medal.[15][16][17] Wellbrock also co-hosted a swimming clinic at the venue of the World Championships,
Etihad Arena, with
Anthony Ervin of the
United States.[18]