During the first few months of 1553, Edward VI, under the influence of the Duke of Northumberland, had made an amendment to his Devise for the Succession in which he disinherited his half-sisters Mary and Elizabeth and named Jane his heir. By the May of that year and as part of his master plan Northumberland arranged the marriage of his son Guildford to Jane.
Two months later, the boy king was dead and Jane was proclaimed queen and in a surprising act of defiance refused to allow Guildford to be named king, therefore scuppering Northumberland's plans to control both Jane, Guildford and England. Soon after events took a downturn with surprising speed. By July Jane was deposed, by November she had been tried and found guilty and by the beginning of February, she was awaiting the day of her execution.
You can see the couple played here by Helena Bonham Carter and Cary Elwes in the 1986 film Lady Jane (which I quite liked but many didn't)