Some account of Ser Giovanni is given in Dunlop's History of Fiction, 3rd ed. 1845, p. 247. He was a Florentine notary, who began his Tales in 1378, at a village in the neighbourhood of Forli. His work is called Il Pecorone, i.e. the Dunce, 'a title which the author assumed, as some Italian academicians styled themselves Insensati, Stolidi, &c., appellations in which there was not always so much irony as they imagined.' The first tale of the tenth Day is thus analysed by Dunlop: 'Story of the Princess Denise of France, who, to avoid a disagreeable marriage with an old German prince, escapes in disguise to England, and is there received in a convent. The king, passing that way, falls in love with and espouses her. Afterwards, while he was engaged in a war in Scotland, his wife brings forth twins; but the queen-mother sends to acquaint her son that his spouse had given birth to two monsters. In place of his majesty's answer, ordering them to be nevertheless brought up with the utmost care, she substitutes a mandate for their destruction, and also for that of the queen. The person to whom the execution of this command is entrusted, allows the queen to depart with her twins to Genoa. At the end of some years she discovers her husband at Rome, on his way to a crusade; she there presents him with his children, and is brought back with them in triumph to England.' Dunlop points out the likeness of this story to those told by Chaucer and Gower, mentions the Lay of Emarè, and adds: 'it is the subject, too, of a very old French romance, published in 4to without date, entitled Le Roman de la Belle Helene de Constantinople. There, as in Emarè, the heroine escapes to England to avoid a marriage, &c. At length she is ordered to be burnt, but is saved by the Duke of Gloster's niece kindly offering to personate her on that occasion.' The story appears again in a collection of tales by Straparola, in the fourth tale of the first night; but Straparola merely borrowed it from Ser Giovanni. See Dunlop, Hist. Fiction, 3rd ed. p. 268.
A very similar story is told in the Roman de la Manekine, by Philippe de Reimes, edited by F. Michel for the Bannatyne Club in 1840. For a brief analysis of this story, see Bibliographia Britannica Literaria (Anglo-Norman Period); by T. Wright, p. 344.
Ten Brink bids us observe the strong Christian element in the original story. Constance herself is almost a personification of the Christian Church, afflicted and persecuted, but at last victorious.
It occurs to me that Shakespeare, in delineating Imogen, did not forget Chaucer's portrait of Constance.
§ 38. We must now compare Gower's version of this Tale with Chaucer's, which at once raises the question as to priority of composition; and there can be little doubt that, as a matter of fact, Chaucer's story was written first. We must first of all notice that both stories really existed in two editions; and it is precisely this fact that makes caution necessary. Most likely, Chaucer first wrote his story about 1380 or even earlier, and revised it about 1387. But meanwhile Gower had been busy with his Confessio Amantis, which was certainly written before 1386, and seems to have been in hand in 1382-5; see Dr. Pauli's preface to Gower, pp. xxviii, xxxii. It was revised, as Gower himself tells us, in the sixteenth year of king Richard II., i.e. in 1392-3. From this the order of things readily appears, and may conveniently be tabulated as follows:—
(a) Chaucer's first edition; ab. 1380.
(b) Gower's first edition; ab. 1382-5.
(c) Chaucer's second edition; ab. 1387.
(d) Gower's second edition; ab. 1393.
We can hence understand what happened. After Chaucer had written his story, he doubtless lent Gower, then his particular friend, a copy. Gower took advantage of the occasion to introduce some expressions which certainly give the impression that he copied them; for several of these verbal resemblances occur in places where there was little or nothing in the original to suggest the phrases which he actually used. Lücke (in Anglia, xiv. 183) gives twenty-seven examples of this, and draws what is, in my opinion, the erroneous conclusion, that it was Chaucer who copied Gower; which seems like suggesting that Tennyson was capable of borrowing from Martin Tupper.