In May 1536 the marriage of Thomas Howard (age 25) and [his wife] Margaret Douglas Countess Lennox (age 20) was discovered by King Henry VIII (age 44). She, Margaret Douglas Countess Lennox (age 20) was next in line of the succession at the time of the discovery. Henry promptly enacted retrospective legislation and imprisoned both Thomas and Margaret in the Tower of London [Map]. Thomas was attainted and remained in the Tower of London [Map] until his death a year later.

Hall's Chronicle 1536. Around Jun 1536. In the Parliament season Lord Thomas Howard (age 25) without the King’s assent affianced the Lady [his wife] Margarete Douglas (age 20) daughter to the [his mother-in-law] Queen of Scottes (age 46)Margaret Tudor Queen Scotland (age 46) and near to the King (age 44) for which presumptuous act he was attainted of treason, and an Act made for like offenders, and so he died in the Tower [Map], and she was long there as a prisoner.

18 Jul 1536. Attainder of Lord Thomas Howard 1536 28 Hen 8 c24 by which Thomas Howard (age 25) was attainted for having married the King's (age 45) niece [his wife] Margaret Douglas Countess Lennox (age 20) in secret thereby attempting to "interrupt ympedyte and lett the seid Succession of the Crowne" (she, Margaret Douglas Countess Lennox (age 20), was heir to the throne at the time). The Act sentenced Howard to death although it wasn't implemented.

Wriothesley's Chronicle 1537. 31 Oct 1537. This yeare, on All Hallowe Even, the Lord Thomas Howarde (age 26), brother to the [his half-brother] Duke of Northfolke (age 64), died in prison in the Tower of London, and his bodie was caried to Thetforde, and there buried.

Allso the Ladie [his wife] Margarett Duglas (age 22), that had lyen in prison in the Tower of London for love betwene him and her, was pardoned by the King and sett agayne at her libertie; howbeit, she tooke his death very heavilie.¹

Note 1. In 1644 she married Matthew fourth Earl of Lennox (age 21), and became Conntess of Lennox, and mother of Darnley.