When Elizabeth I succeeded her half-sister Mary as Queen of England in 1558, her accession was disputed due to the questioned legitimacy of the marriage of the Queen's parents - Henry VIII and Anne Boleyn. Under Henry VIII and his advisor Thomas Cromwell, power was gradually shifted from regional institutions to royal control. This course was encouraged by Elizabeth's counsellors such as William Cecil and a policy of centralization was the approach favoured by Elizabeth herself at least in regards to the northern border region. Opponents of Elizabeth looked to Mary, Queen of Scots, as the descendant of Henry's sister Margaret Tudor. The claims were initially put forward by Mary's father-in-law, King Henry II of France, but Mary upheld them after her return to Scotland in 1561. Many English Catholics, then a significant portion of the population, supported Mary's claim as a way to restore Catholic ideology. This position was especially strong in Northern England, where several powerful nobles were Catholics; there had been similar risings against Henry VIII; the Pilgrimage of Grace of 1536 and Bigod's Rebellion of 1537. Supporters of Mary hoped for aid from France  and possibly Spain . Mary's position was strengthened by the birth of her son, James, in 1566 but weakened again when she was deposed in July 1567.
Question: How many years does Mary's position was strong?
Answer: 1