Excerpts from Books and Wikipedia
"Ever since her impetuous flight to England twenty years before, Mary had been a thorn in Queen Elizabeth's side. As a descendent of King Henry VII through his daughter Margaret Tudor, Mary was next in line to the English throne. For the Catholic minority in England she was the rightful queen, and so long as she remained at liberty would be the focus of plots to restore England to Catholic rule." [Furtado: 1001 Days]