Take the Keys & Lock Them Up  the topic so nice, I did it twice more lengthy royal imprisonments   James I of Scotland (17 years, 10 months) This is the longest period for a ruling monarch to be imprisoned. James was a wee laddie of 11 when captured at sea in 1406 as he was being sent to safekeeping in France. His father died the same day. England's Henry IV 1st kept him confined at the Tower of London, then at Nottingham Castle, though occasionally Henry allowed him to go on progress with his court. He wed the king's half-sister, Lady Joan Beaufort, promptly upon his release in 1424.   Edward, Earl of Warwick (15 years, 6 months) Son of George, Duke of Clarence, & nephew to Edward IV & Richard III, Edward was arguably heir to the throne after Edward IV's two sons, the legendary Princes in the Tower, & taken into custody at Sheriff Hutton Castle in 1484. Upon Henry VII's defeat of Richard at Bosworth, young Warwick, aged 10, was transferred to the Tower of London where he was kept confined. He was never educated & was believed to have been simpleminded. The Tudors occasionally trotted him out for display when a pretender laid claim to the throne & had him executed in November 1499, aged 24.   Duncan II of Scotland (15 years) At age 12, this eldest son of Malcolm III was taken hostage in 1072 by William I as surety against his father's promise not to raid the north of England. Malcolm continued to harass the Normans & disinherited his son, who was kept in various places in England & Normandy until 1087. The Normans supported him in his quest to regain the Scots throne in 1094, but his kingship lasted a scant 6 months before he was killed.   Gruffydd ap Cynan of Gwynedd (12 years) Exiled to Ireland in his youth, Gruffydd spent 6 years attempting to regain the throne of Gwynedd & suceeded in 1081. Unfortunately, he did not get to enjoy the fruits of his labors, as he was captured by a Norman force at Corwen & held at Chester until his release in 1094.   David II of Scotland (10 years, 11 months, 17 days) Only son & heir of Robert the Bruce, David, who succeeded to the throne aged 5, was deposed two years later by Baliol forces & then restored briefly until Edward III's trouncing of the Scots at Halidon Hill. He stayed in exile in France until he led a Scots invasion of England in concert with the French as part of the Hundred Years' War. He was captured at the battle of Neville's Cross in 1346 & remained an English prisoner until he was released under the terms of the Treaty of Berwick in 1357.