The timeline Fidei Defensor (Defender of the Faith) examines the effect on history of an early death of Henry VIII, even before he can take the English throne. The cause of his untimely demise is tuberculosis, which he contracts from his brother Arthur, Prince of Wales, some time between 1495 and 1502. Though Arthur dies on the 2nd of April 1502 (exactly as OTL), Henry is finally done in by the disease September 2, 1503. This leaves Margaret Tudor as the next heir to Henry VII and the English Crown. Amazingly, only a month before Henry's death, Margaret was married to James IV, King of Scotland as part of the Treaty of Perpetual Peace (1502). Though many in the royal court were staunchly opposed to this when they saw the ailing Henry's health, the nation was bound by the treaty to go through with the marriage.
On March 24, 1509, King Henry VII of England died (early due to stress) of tuberculosis in Richmond Palace and was soon buried in Westminster Abbey. Immediately, former speaker of the House of Commons Edmund Dudley sent a messenger to King James IV, informing of the King of England's death. James for his part had already been prepped by both English and Scottish nobles since Henry fell into ill health, and had just left Edinburgh for London in April 5. Relieved that the succession triggered neither unrest nor an invasion, the people of London flocked to greet their new monarch as he entered the city on 9 May. At last on May 25th he was crowned James IV and I, By the Grace of God, King of England, Scotland and France, Lord of Ireland and Lord of the Isles.
Not only did James inherit his father-in-law's personal fortune of £1.25 million (£648 million in OTL 2010), but by an act of both Parliament's in May 19, the substantial treasuries of both kingdoms were technically, though not in name, combined into one. This made the Crowns of Scotland and England in personal union, through the monarch, for the first time in history.