This video says about itself:
This giant alien-like fish is called the Ocean Sunfish, Moon Fish, or Mola mola. They are heaviest of all bony fish and can be found in oceans all over the world. Fully grown adults can weigh over 5,000 pounds and grow up to 14 feet from top to bottom, and 10 feet wide, but unlike most fish, they actually have no tails.
17 December 2015 – If one strolls along the beach in December or January, one has a reasonable chance of finding a sunfish. The first sunfish of the season has already been found again, in Hooksiel in the German Wadden Sea, at the Weser river estuary, on 12 December. The previous one was on January 14 of this year, on Texel.
At this time of the year sunfish migrate from north to south. Then, they have the possibility to end up in the North Sea. The fish are accustomed to oceans and have no experience in shallow water. Thus it happens that they helplessly, but still alive wash ashore on the southern beaches of the North Sea.
Sunfish beached on Texel: here.