Recently I have come across two online articles about research into a detail in the Melun Diptych which dates from the early 1450s. The painting was commissioned by Étienne Chevallier, secretary and subsequently Treasurer to King Charles VII, in memory of his wife who died in 1452, and painted by Jean Fouquet. There is a biographical note on Wikipedia about the former at Étienne Chevalier and a much longer illustrated article about the artist and his work at Jean Fouquet
The two panels were sold in 1775 to fund renovations to the church in Melun to which it had belonged and the two panels are now in galleries in Berlin and Antwerp.
The diptych is described in a Wikipedia article at Melun Diptych
The model for the figure of the Virgin Mary is usually identified as having been King Charles VII’s mistress Agnès Sorel, who had died in 1450. She had been the first maîtresse-en-titre of a French king, and there is a Wikipedia account of her life at Agnès Sorel
Surroging the Virgin and Child are Seraphim and Cherubim, the two highest orders of Angels.The Seraphim are shown in red as the are burning with the love of God. The next rank of Angels are the Cherubim who contemplate Him with ice-cold logic.
The new research concentrates on the stone which St Stephen has as his emblem of martyrdom on the book in his left hand. The argument is that this is not just any rock but a prehistoric stone axe head. The articles can be seen at What's That Oddly Shaped Stone in a 15th-Century Painting? from Hyperallegenic, and at This 15th-Century Painting Might Actually Depict a Prehistoric Tool, New Research Suggests
The church for which the diptych was originally commissioned is discussed briefly at Collegiate Church of Notre-Dame, Melun