Where is the only memorial to a British king on German soil?

The only British king that I know of who has a statue in Germany is King George I of the UK, who was also the Elector (ruler) of Hannover and has a statue there, as shown in the images at the link:
https://en.wikipedia.org/wiki/George_I_of_Great_Britain
https://commons.wikimedia.org/wiki/File:Georg_I._Ludwig_(George_Louis),_Kurf%C3%BCrst_von_Braunschweig-L%C3%BCneburg,_K%C3%B6nig_von_Gro%C3%9Fbritannien_und_Irland_und_Titulark%C3%B6nig_von_Frankreich,_Skulptur_vom_Bildhauer_Carl_(Karl)_Rangenier,_um_1862,_Welfenschloss_Hannover.jpg

The son of George I of England was George II - the last British monarch to be born outside of Britain (in the city of Hanover). George II had a monument in the city of Döbeln, located in Saxony.

döbeln.de/html/nmkg_10.html [no longer exists]
döbeln.de/html/konig_georg_ii_denkmal.html [no longer exists]

In 1940, however, the monument was demolished in order to use the metal for arms and ammunition.

Unfortunately, the monument identified by wellenbrecher is not (or was not, since it was melted down during WWII) a monument to King George II of the United Kingdom, but rather a monument to King George of Saxony, who was the next-to-last member of the House of Wettin to rule over Saxony (the monarchy ended in November 1918 because of the defeat of Germany in WWI). The monument was erected in 1911, during the reign of his son Frederick Augustus III (the last king of Saxony, who, as the commentary notes, attended the unveiling of the statue). The postcard picture linked above correctly identifies this as the "King George monument". Here is a translation of part of the German commentary in the other link above:

"If a people were connected to a princely house through mutual loyalty and love for centuries, as our people were to the Wettin house, then these feelings will not be erased if the historical development makes a dash under the past.... If one erected a worthy monument to the father of the last Saxon king in Döbeln, it would mean a debt of thanks.... King George had quite a few opponents, but no one could deny that it was particularly thanks to his conscientiousness that Saxony's finances were put in order."

So this monument has no connection whatsoever to the United Kingdom monarch.
https://en.wikipedia.org/wiki/George,_King_of_Saxony

Thanks, AyatollahK, for the explanation. So the monument of King George I seems to be the only one on German soil. However, was is built after George became King of Great Britain? Or was it made to honour George as the Duke of Brunswick-Lüneburg rather than as a king?

Interestingly, there is also a statue in Hannover to a British born king who was not the king of Great Britain. This was Ernst August, fifth son of George or Georg III, who succeeded his brother Wilhelm IV, whereas the British crown went to William IV's niece Alexandrina (better known as Victoria) who could not succeed in Hannover. So at the start of George I's reign, Great Britain (not forgetting Ireland held as part of the English realm) had a German born king, and at the start or Victoria and Ernst August's reigns, Hannover had a British born king. Born in Buckingham House, in fact. Pics of Ernst's statue at https://equestrianstatue.org/august-ernst-die-g-ttinger-sieben/ Until the birth of Prince Albert Jr (better known as Edward), Ernest Augustus was the first in line for the British throne after Victoria's accession.

Translated from German Wikipedia about William IV.

Fort Wilhelm, built in Bremerhaven in 1834, was named after him, as was Mount William in the Antarctic and the former Wilhelmsbrücke in Lower Saxony.

As rector of the University of Göttingen, he donated the auditorium for the secular celebration in 1837. As a thank you, the space in front of the auditorium was renamed Wilhelmsplatz. In addition, the people of Göttingen erected a memorial to the king on this square, which to this day is the only memorial on German soil for a British king, who, however, was also King of Hanover.

https://de.m.wikipedia.org/wiki/Wilhelm_IV._(Vereinigtes_Königreich)