Botanists, Gardeners - I need your help!

Dear You, 
this might better belong into my blog http://gardeninginhighheels.blogspot.de/, but here I might reach more people.
In August on our stay on the German Northsea island Sylt I found a little flower that I have never seen before.
It is tiny - the blossom is about 2,5cm in diameter, hight of the whole plant about 5 - 6 cm, and on the second picture you can see its dentated leaves. It is strongly blue (almost like the colour of gentian - which it definitely is not). Striking white round stamen.
It was very stormy, so the photos with my macro are not as sharp as I wanted them to be.
I found the flower in the village Keitum - the tideland side of Sylt. Only one single plant, near a pathway. Might have escaped from a garden (in the 19th century there was a captain in Keitum who was famous for collecting exotic flowers).
The next day I first thought that some nitwit had nicked it - but it was still there, torn by the storm that had raged in the night.

Now: I know quite many wild and garden flowers - but I am baffled here. Can you please help me?