In March of 1849, Poe republished his 1846 Valentine poem to Frances Osgood. He rewrote the poem--an acrostic containing her name--correcting the earlier version's misspelling of "Sargent." This necessitated a complete revision of the latter half of the poem, and in doing so Poe did a very curious thing. The last few lines of the 1849 poem refers to Osgood's "well-known name" and says of it:
"Its letters, although naturally lying--
Like the knight Pinto (Mendez Ferdinando)--
Still form a synonym for truth. Cease trying!
You will not read the riddle though you do the best you can do."
Ferdinando Mendez Pinto was a sixteenth-century traveler who was regarded as a famous teller of lies. His name, in fact, became so associated with falsehoods that the saying was that he only told the truth when he admitted to being a liar--only by confessing his many tall tales did his name become a "synonym for truth." Interestingly, Poe's enemy Charles Briggs used the pseudonym "Ferdinand Mendoza Pinto," to write a series of columns for a New York paper--a pen name Poe dryly described as "apt."
In other words, by writing that Frances Osgood's name, like Pinto's, was a "synonym for truth," he was publicly calling her a liar. Which casts a fascinating, and completely ignored, light on their relations.