In writing The Two Gentlemen of Verona, Shakespeare drew on the Spanish prose romance Los Siete Libros de la Diana (The Seven Books of the Diana) by the Portuguese writer Jorge de Montemayor. In the second book of Diana, Don Felix, who is in love with Felismena, sends her a letter explaining his feelings. Like Julia, Felismena pretends to reject the letter, and be annoyed with her maid for delivering it. Like Proteus, Felix is sent away by his father, and is followed by Felismena, who, disguised as a boy, becomes his page, only to subsequently learn that Felix has fallen in love with Celia. Felismena is then employed by Felix to act as his messenger in all communications with Celia, who scorns his love. Instead, Celia falls in love with the page (i.e. Felismena in disguise). Eventually, after a combat in a wood, Felix and Felismena are reunited. Upon Felismena revealing herself however, Celia, having no counterpart to Valentine, dies of grief.
Diana was published in Spanish in 1559 and translated into French by Nicholas Collin in 1578. An English translation was made by Bartholomew Young and published in 1598, though Young claims in his preface to have finished the translation sixteen years earlier (c. 1582). Shakespeare could have read a manuscript of Young's English translation, or encountered the story in French, or learned of it from an anonymous English play, The History of Felix and Philiomena, which may have been based on Diana, and which was performed for the court at Greenwich Palace by the Queen's Men on 3 January 1585. The History of Felix and Philiomena is now lost.
Another major influence on Shakespeare was the story of the intimate friendship of Titus and Gisippus as told in Thomas Elyot's The Boke Named the Governour in 1531 (the same story is told in The Decameron by Giovanni Boccaccio, but verbal similarities between The Two Gentlemen and The Governor suggest it was Elyot's work Shakespeare used as his primary source, not Boccaccio's). In this story, Titus and Gisippus are inseparable until Gisippus falls in love with Sophronia. He introduces her to Titus, but Titus is overcome with jealousy, and vows to seduce her. Upon hearing of Titus' plan, Gisippus arranges for them to change places on the wedding night, thus placing their friendship above his love.
Also important to Shakespeare in the composition of the play was John Lyly's Euphues, The Anatomy of Wit, published in 1578. Like The Governor, Euphues presents two close friends who are inseparable until a woman comes between them, and, like both The Governor and Two Gentlemen, the story concludes with one friend sacrificing the woman so as to save the friendship. However, as Geoffrey Bullough argues "Shakespeare's debt to Lyly was probably one of technique more than matter." Lyly's Midas may also have influenced the scene where Launce and Speed run through the milkmaid's virtues and defects, as it contains a very similar scene between Lucio and Petulus.
Other minor sources include Arthur Brooke's narrative poem The Tragical History of Romeus and Juliet. Obviously Shakespeare's source for Romeo and Juliet, it features a character called Friar Laurence, as does Two Gentlemen, and a scene where a young man attempts to outwit his lover's father by means of a corded ladder (as Valentine does in Two Gentlemen). Philip Sidney's The Countess of Pembroke's Arcadia may also have influenced Shakespeare insofar as it contains a character who follows her betrothed, dressed as his page, and later on, one of the main characters becomes captain of a group of Helots.