Almost bought an unknown Rubens' drawing

Marquis-Olivier, from France, sells on 16 December 2017 a "Flemish School, 17th century" drawing (sanguine) of "Angels adoring the Virgin", estimated at 200€ (they first offered it a month ago with a 400€ estimate, but I guess it didn't sell then).

At first, I was very excited about this drawing, as it looked like a work by Rubens, a sketch for his Vallicella Madonna (of which different versions exist).

The drawing is similar enough to be clearly about the same work, but different enough not to be a copy after it but some design for it.

The quality of the drawing was good (though not superb), and the style was typical for Rubens' in his Italian period.

Luckily I contacted someone who knows a lot more about Rubens. At first they were enthusiastic (but realistic), and agreed that this could well be an unknown and unrecognised drawing by Rubens.

But just days before the sale, they came back with bad news: it is almost certainly a copy after all, not after a painting, but after an authentic drawing by Rubens kept in the Albertina in Vienna. That drawing is nearly identical to the one for sale, but better in its execution. They may still be two versions of the same design, with perhaps the one for sale slightly earlier, but the more likely explanation is that the one for sale is a copy after the one in the Albertina (perhaps at best a workshop copy from Rubens' time). So in the end we decided, with some regrets, not to go for it.

And that's how I almost bought an unknown Rubens' drawing!