I was interested to learn that the silver leaved Brunnera often have offspring that are fairly similar. I tried to grow some seeds but no luck.
However this year I have found a few seedlings, I am keeping the ones with some silver markings. The colouring is not very consistent between different leaves and the silver effect is sometimes only partial. The plan is to keep the best ones and hopefully gradually get some nice looking plants. Don't know how fast they grow, not very fast so far.
They were close to the Brunnera macrophylla 'Silver heart' and Brunnera macrophylla 'Hadspen Cream' so it is is possible that they are a cross or just from one of them. I suppose the Brunnera macrophylla 'looking glass' is only a short bee flight away too.