Continuing to read books that deal with the fates of the princes in the tower, I turned to another book on my TBR shelf, Vanora Bennett's Portrait of an Unknown Woman - a complex novel based in part on the theories of amateur art historian Jack Leslau  about hidden meanings in a portrait of the family of Thomas More, painted by Hans Holbein (who was known for the use of multiple levels of symbolism in his mature work).
The theory here is that the two young princes were taken from the Tower, raised for some years by Sir Tyrell, and then given new names and identities through the intervention of Bishop John Morton - in whose household the young Thomas More served as a page. The elder prince, Edward V, is alleged to have been adopted into the noble Guildford family and to have quietly accepted his fate, perhaps due to a belief that the charge of illegitimacy made against him and his siblings was true. (In this context, it's interesting to note that one of his grandsons, Guildford Dudley, was married to Lady Jane Grey in a plot to usurp the throne of Mary Tudor, and another grandson, Robert Dudley, was the favourite of Queen Elizabeth I and is believed to have hoped to marry her.) This novel, however, focuses on the younger prince, Richard, who is sent to the mainland to become a scholar under the protection of his aunt, Margaret of Burgundy. Given the name John Clement, he eventually becomes part of the loose circle of humanists that included Erasmus and Thomas More, and on his return to England becomes part of More's large, loosely connected household, and later still, marries More's ward and relative Margaret Giggs.
Portrait of an Unknown Woman, told largely from the perspective of Margaret Giggs Clement, with some sections from the viewpoint of Hans Holbein, is largely the story of Margaret's relationships with three men: her adoptive father Thomas More, as he becomes less the humanist and more the defender of Catholicism against heresy in the face of the growing power of the reformist-minded Boleyns at court; painter Hans Holbein who comes to England with the support of More's friend Erasmus, seeking help from More in finding patrons at the English court; and her husband, John Clement, scholar and physician, a protégé of her father's despite being of an age with him, and secretly the lost prince of York.
Now it's important to note that all these people - not just Thomas More, Erasmus and Hans Holbein, but also Edward Guildford, John Clement and Margaret Giggs, were real people who, insofar as the historical record survives, did the things that they are shown as doing in this novel. The invention lies in the attribution of a secret identity to Clement and the knowledge of it to various of the characters, including More, Erasmus, and eventually Margaret.
Even without the lost princes theme, Portrait of an Unknown Woman works well both as a portrait of the family and inner circle of Thomas More, and, in later chapters, as an introduction to the symbolic complexities scholars have found in Holbein's art - though it must be pointed out that there is little support for Leslau's specific interpretation of the More family portrait. Bennett's portrayal of More as a man driven by deep inner conflicts between secular and spiritual desires, drawn into an almost fanatical persecution of heretics, and an ultimate longing for martyrdom, is a complex and fascinating one, and yet it never overshadows the voice of his adopted daughter Margaret Giggs, whose story of love, faith and the middle road between devout Catholicism and a healer's compassion is compelling.
The load of imagined secrets gives the later chapters of the book a tinge of melodrama that weakens the otherwise strong narrative, but overall, it's quite a good read.
 For more on Leslau's theories, this is a solid but not too exhaustively detailed overview: https://mattlewisauthor.wordpress.com/