One of the pen-and-ink drawings (above) is the only surviving study for his important painting, The Lamentation, which is in the Koninklijk Museum, Antwerp.
The importance of the drawings was overlooked by a Paris auction house, which catalogued them as being from the 'circle of Van Dyck'. The sheet had long been in a minor French collection.
The buyer at the Paris sale sold the sheet on to Hazlitt, Gooden & Fox, leading London dealers, who immediately suspected the Rubens connection.
The attribution was confirmed by Michael Jaffe, the respected scholar, and the drawings dated to between mid-1617 and mid-to-late 1618.
The drawings, which are priced at 'several hundreds of thousands', give an insight into the 17th-century Dutch master's working methods. Several details reflect how Rubens changed his mind - Professor Jaffe points out, for example, that in the drawing, Mary Magdalene kneels to kiss Christ's left hand, whereas in the painting, she stands, with hands clasped, to grieve beside the Madonna.