While there's no doubt that rumors circulated about the parentage of young Edward, especially in the late 1450's as Yorkist propaganda heated up, there is no evidence, other than gossip, that Edward of Lancaster was the son of anyone other than Henry VI. As both R.A. Griffiths and Helen Maurer have pointed out, the Parliament Rolls for 1455 indicate that Richard Tunstall, an esquire of the body, had previously received a handsome annuity for bringing the king the news of the queen's pregnancy:
Provided also that this petition and act of resumption shall not extend or be prejudicial to our letters patent and grant made by us to Richard Tunstall, knight, by the name of Richard Tunstall, esquire for our body, of 50 marks a year for term of his life, part of an annuity of £40 a year, granted by us for term of his life, to be taken from the issues, profits and revenues of our manors, lands and tenements, and from our other possessions within our county of Lancaster, by the hands of our receivers there at the time: because, among other things, the said Richard gave us the first comforting report and news that our most entirely beloved wife the queen was with child, to our most singular consolation, and a great joy and comfort to all our true liege people.
Maurer also notes that Henry bought a jewel called a "demy ceynt" for Margaret while she was pregnant and that Margaret received generous grants in July 1453, which she suggests were made by Henry as a reward for her pregnancy. It certainly seems unlikely that they would have been made had the king suspected that Margaret was carrying another man's child.
Once Henry recovered from his first episode of mental illness, his reaction to his son was one of pleasure. As the Paston Letters indicate:
Edmund Clere to John Paston.
January 9, 1455.
Right welbeloved cosyn,—I recomaund me to you, latyng you wite such tidings as we have.
Blessed be God, the King is wel amended, and hath ben syn Cristemesday, and on Seint Jones day comaunded his awmener to ride to Caunterbury with his offryng, and comaunded the secretarie to offre at Seint Edwards.
And on the Moneday after noon the Queen came to him, and brought my Lord Prynce with her. And then he askid what the Princes name was, and the Queen told him Edward; and then he hild up his hands and thankid God therof. And he seid he never knew til that tyme, nor wist not what was seid to him, nor wist not where he had be, whils he hath be seke til now. And he askid who was godfaders, and the Queen told him, and he was well apaid.
. . .
And my Lord of Wynchestr and my Lord of Seint Jones were with him on the morrow after Tweltheday, and he speke to hem as well as ever he did; and when thei come out thei wept for joye. And he seith he is in charitee with all the world, and so he wold all tho Lords were. And now he seith matyns of Our Lady and evesong, and herith his Masse devoutly . . .
But what of the old story, that crops up in many historical novels and even in some nonfiction, that Henry VI, unable to comprehend how he could have been the father of Margaret's child, declared that it must be the work of the Holy Spirit? This story comes from a dispatch on March 27, 1461, from Prospero di Camulio, Milanese Ambassador in France, to Francesco Sforza, Duke of Milan. Writing from Brussels about the latest English news, Camulio reported that it was being "said that the King of England had resigned his crown in favour of his son, although they say his Majesty remarked at another time, that he must be the son of the Holy Spirit, etc." What writers who latch onto this tasty morsel of a statement almost never quote is the rest of Camulio's sentence: "but these may only be the words of common fanatics, such as they have at present in that island." Certainly the timing of this gossip, current just a few weeks after Edward IV had taken the throne, should make us suspicious, as it did Camulio.
Those who maintain that Henry VI was not Edward's father often point to the eight-year delay between the couple's marriage in 1445 and the birth of Edward in 1453; they suggest that a desperate or simply wanton Margaret, having given up on Henry's capabilities, recruited another man to beget a child upon her. But the gap between marriage and pregnancy could be explained by other factors, such as subfertility, and is hardly indicative in itself that Margaret resorted to adultery to produce a child. Notably, Cecily of York, who seems to have married her husband no later than 1429 when she was 14 and he was 18, did not have her first child, Anne, until 1439. Despite this lengthy delay, no one has suggested that Anne was anyone other than the Duke of York's child. It seems only fair to give the Red Rose the same benefit of the doubt as the White Rose.