Deleted member 5909
Complicated. English Common law lacked the mechanisms for civil legitimisation via letters patent, as in France, Castile and other realms with legal systems heavily influenced by Roman Law. The only precedent I know of is John of Gaunt, whose children by his mistress (whom he subsequently married) were legitimised by a papal bull, which was later clarified by Parliament.
As papal decree wouldn't be possible in this case, an act of parliament could certainly do so. However, in truth, it wouldn't have been necessary. The Second and Third Succession acts passed during Henry VIII's reign already gave him the power to will the Crown and modify the line of succession by letters patent or testament, provided it did not infringe on the rights of his legitimately born heirs of the body. It was already reported by Chapuys in 1536 that FitzRoy would likely have been named heir presumptive under the terms of the Second Act, had he not been on his death bed at the time with terminal consumption. So, it's not too much of a stretch to envision him being included in the line of succession after Edward in this scenario's version of the Third Act of Succession, given that this law also reinstated Elizabeth and Mary, but reiterated their status as bastards.
Agreed: The effects of a surviving FitzRoy are going to create a great deal of butterflies, to the point that even the marriage to Anne of Cleves may or may not be butterflied away, and we could very well see a different girl put into play by the Norfolk and FitzRoy to replace OTL's Catherine Howard.
One thing that hasn't been mentioned so far: If FitzRoy allies with the Howards (very likely, given he was wed to Norfolk's daughter and very close with his brother-in-law, Surrey), he's going to be part of the Anti-Cromwell faction at court the sprang up in the events following Anne Boleyn's downfall. With the opposition of FitzRoy, a man who conceivably will be very close to his father, Cromwell may fall sooner rather than later, butterflying away Anne of Cleves. And, even if events go more or less as in OTL, we could very well see a different girl put into play by the Norfolk and FitzRoy to replace OTL's Catherine Howard.
Which brings me to my next point: The assumption thus far in this thread seems to be that a surviving FitzRoy would have Reformist sympathies, in line with his royal half-brother and the Seymours. I don't see this as a given by any means.
FitzRoy grew up before the Supremacy and was raised in the Old Religion (unlike Elizabeth and Edward, whose religious views were connected in no small part to the climate of their respective childhoods); there is even some evidence from the letters of Lady Bryan that, after he came to court in 1525, FitzRoy was brought up for a time with Mary in the royal nursery, which means that they may or may not have shared tutors; and even so, we do know that his education was supervised by Wolsey and his father.
It's also worth mentioning that he had very large landholdings in the North Country--so much so that he held nominal presidency of the Council of the North, with the contemporary assumption being that he would govern there when he came of age (I assume similar to the role Richard III had played in Edward IV's reign)*. This may possibly give him ties to a lot of other very anti-reformist families in this scenario.
If FitzRoy is aligned with the Howards and a player in Cromwell's downfall, it is likely that he'll then continue to align with Norfolk, Gardiner and other members of the 'conservative' faction which arose in the aftermath (made up largely of members of the old nobility and other men opposed to further religious reform). This probably creates enough butterflies to keep the conservative party in power and prevent the post-1546 situation, which led to Seymour's rise with other reformers, such as Sir Anthony Denny and John Dudley.
Taking all this into account, the situation in the winter of 1547, when Henry VIII dies (assuming he expires more or less at the same time in this scenario), will be a very different one indeed than from OTL's, especially if the downfall of the Howards is butterflied away entirely. Whether or not FitzRoy will be named Lord Protector is debatable. I see a regency council being more likely as in Henry VIII's OTL will, since this seems to be the trend in English royal minorities. However, the Council in such a scenario would include not only FitzRoy, but others such Gardiner (likely excluded in OTL by the mechanisms of Seymour and others), Wriothesly and Norfolk. The Seymour brothers probably would be included as well, though they likely won't have the power they had in OTL's 1547 for a number of reasons.
Given his status as next-in-line to the Crown, his record as a tried military commander (against the Scots in the Rough Wooing, see the note below) and his relatively large power base, FitzRoy would be in a good position to pull off a similar coup to OTL's Seymour and assume power as Lord Protector.
This said, even if FitzRoy and the 'conservative' faction dominate the regency of Edward VI, I don't see reconciliation with Rome as likely, since it contravenes FitzRoy's interests as: (a) it would displace him in the succession and (b) he and many other members of the old nobility have gained a great deal of wealth and land from the Dissolution of the Monasteries (in OTL even Gardiner was wary of reconciliation in Mary's reign because of its potential restoration of monastic land). More likely, we'll see a continuation of the Henrician Church as it stood in Henry VIII's final years in OTL (such as retaining the Six Articles and the Act for the Advancement of True Religion).
*On a side note, this also means that Seymour probably won't be a leading military commander in the Rough Wooing, since FitzRoy would be a more natural choice for the role (I believe he served in the office of Lord Warden of the Marches), which may make Seymour less powerful ITTL, as a great deal of the credibility that allowed him to pull off the coup of 1547 came from his successful campaigns against the Scots.
