Jan Frans Beschey: artist of a 1750 portrait or dealer of a 1650 portrait?

Cuxhavener Auktionshalle, from Cuxhaven, Germany, sells on 29 October 2016 a "Jan Frans Beschey" portrait, estimated at 280 Euro. At the time of writing, it had already gotten 5 bids and was now at 530 Euro.

Jan Frans Beschey (1717-1787) was the youngest of the 4 painting Beschey brothers, and probably the least well-known. Balthasar, his teacher, is the most common name of them, the other two (Karel and Jacob Andries) are fairly obscure. . His name is also given as Jan François, Jean François, and Jan Franciscus. He worked for most of his adult life as an art dealer in London. After his death, a collection of 250 artworks was sold in Antwerp.

Jan Frans is usually associated with populated landscapes, which sell for 5,000 to 10,000 Euro. His portraits are less common, I could only find two examples: one was a portrait of a man (perhaps GF Handel), sold at Christie's in 2003 for $1,600, and the other is only attributed to Beschey (and seems more caricatural than his other works), and is kept in the amusingly named Royal Mineral Water Hospital.

The work at auction is signed on the frame, "Jan Francis Beschey / Antwerp". The English name for Antwerpen makes sense since he operated in England. I don't know whether he may have signed works he sold and framed in this way though, so whether this may be more logical as a retailer mark instead of a painter mark. If this is the case, then we have an interesting piece of evidence for his activities as a dealer, and an anonymous portrait.

The painting also has the remnants an intriguing label on the back. While these are often faked or later additions, it is always interesting to try to decipher them anyway, as they may contain valuable clues. "Le Prin... ...lones ...Va..k..." Not much useful there; apparently a portrait of a princess, and one would like to read "van Dyck" at the end of the second line, but that's wishful thinking.

Taking all of these clues together, and condisering the  style of the painting and the look of the sitter, I tend to believe that this is however not a painting by Beschey, but a much older painting sold (and perhaps reframed) by Beschey. It may be a portrait of a princess, and reminds me of similar depictions of Henrietta Stuart or Mary Stuart. It should be dated ca. 1650. It isn't by one of the great masters of the period, but a very pretty, confidently painted portrait nevertheless which should, even without knowing either sitter or artist, easily fetch 1,000 Euro. 

UPDATE: sold for 1,250 Euro, some 5 times the estimate.