With the marriage annulled, there was technically no legal ground to execute Kathryn. Henry VIII knew this and it took until February 7, 1542, for parliament to create a reason. Similar to Thomas Cromwell, a Bill of Attainder was created, which meant that his fifth wife could be executed. The bill stated that a Queen Consort would be found guilty of treason if she didn’t disclose her sexual history within 20 days of the marriage.
It seemed that Henry VIII had believed Kathryn’s story but by failing to tell him that there had been a sexual relationship with Francis, she had condemned herself to death. There was no way around this bill. On February 8, the bill gained royal assent and Kathryn was executed five days later on Tower Hill.
It does beg the question whether Kathryn could have saved her own life. Henry VIII had been embarrassed and he was used to getting what he wanted. This time he didn’t have Cromwell to make it happen, like he did with Anne Boleyn, so needed to find another option. Had she admitted to the pre-contract, it is possible that he would have still found another way around to execute her for the shame and embarrassment she had caused.
In no way am I for or against Henry VIII in this. It was a difficult time to live and Henry was under a lot of pressure to provide an heir. At the same time, he needed a Queen Consort who would not bring shame and embarrassment; a Queen Consort who would be loved by the English people and this would have caused them to turn against her. Henry may have felt he had no choice in the matter.
Kathryn Howard was simply a young girl—only in her late teens/early 20s when she was executed—who had grown up without the supervision of her parents. She was a free-spirit and not fit to be a Queen Consort. The main reason Henry VIII married her was because she was so full of life and excitement. Henry just failed to question her past, knowing where she had grown up.