It has been given special permission to stay open because the king and his entourage were classified in the same way as a household.
It is unclear if the wealthy King's four wives are also staying in the four-star hotel.
Despite the fact that breaking Thailand's lèse-majesté laws by criticising the monarchy can earn you 15 years behind bars, many Thais have expressed fury at the King's extravagance.
A hashtag which translates at 'Why do we need a king?' has been shared 1.2 million times on Twitter since news of King Rama X's stay became public.
The 67-year-old royal is a familiar face in Germany.
He owns property on Lake Starnberg and is also a frequent visitor in Upper Bavaria.
Although the ski resorts are no longer open, the King, who is known for his love of cycling, has made frequent trips around local streets by bike.
King Rama X's trip to the hotel has been allowed to go ahead, despite Bavaria being one of the first German states to go into lockdown.
According to the latest statistics from the Johns Hopkins University, Germany currently has 33,593 confirmed cases of coronavirus, with 164 deaths.
Thailand currently has 1,524 confirmed cases and two deaths.
The King of Thailand has gone into 'isolation' with an entourage of 20 women, according to local reports.
King Maha Vajiralongkorn, known as Rama X, entered the Grand Hotel Sonnenbichl in the fashionable winter sports resort of Garmisch-Partenkirchen in Germany.
With him was a harem of beautiful royal concubines.
German officials lifted quarantine rules on a luxury hotel to allow King Rama X to go on holiday there with his entourage of 20 women.
King Rama X booked out all of the hotel's rooms, German newspaper Bild reported.