sentences:  During the first phase of Queen Mary's reign, Lady Katherine was senior heir-in-line to the throne as Mary was yet unmarried and her younger sister Elizabeth was regarded as illegitimate.Demoted when Elizabeth was declared heir, Lady Katherine's claim came to the fore again when Queen Elizabeth acceded to the English throne in November 1558.At one point the Queen was apparently contemplating Lady Katherine Grey as a potential Protestant heir, with rumours of a possible adoption, but any such development was terminated upon Lady Katherine's clandestine marriage to Lord Hertford.