From the longer Wikipedia page 
Francis II of Brittany (in Breton Frañsez II, in French François II) (23 June 1433 – 9 September 1488) was Duke of Brittany from 1458 to his death. He was the son of Richard of Brittany and the grandson of Duke John V. Francis' life was characterised by conflicts with King Louis XI of France (War of the Public Weal) and with his son King Charles VIII.
Protector of the House of Lancaster Edit
Francis II was protector of the House of Lancaster in exile.
Francis II serendipitously became the protector of England's House of Lancaster in exile from 1471-1484.
During the latter half of the 15th century, civil war existed in England as the Houses of York and Lancaster fought each other for the English throne. In 1471, the Yorkists defeated their rivals in the Battle of Barnet and Battle of Tewkesbury. The Lancastrian King Henry VI and his only son, Edward of Lancaster, died in the aftermath of the Battle of Tewkesbury. Their deaths left the House of Lancaster with no direct claimants to the throne. The Yorkist king, Edward IV, was in complete control of England. He attainted those who refused to submit to his rule, such as Jasper Tudor and his nephew Henry, naming them as traitors and confiscating their lands.
The Tudors tried to flee to France but strong winds forced them to land in the Duchy of Brittany, where they were taken into the custody of Francis II. Henry Tudor, the only remaining Lancastrian noble with a trace of royal bloodline, had a weak claim to the throne, and Edward regarded him as "a nobody." Francis II, however, viewed Henry as a valuable tool to bargain for England's aid in conflicts with France and therefore kept the Tudors under his protection.
In October 1483, Henry launched a failed invasion of England from Brittany. His fleet of 15 chartered vessels was scattered by a storm, and his ship reached the coast of England in company with only one other vessel. Henry realized that the soldiers on shore were Richard III's men, and so he decided to abandon the invasion and return to Brittany. The Duke of Buckingham, who was Henry's main conspirator in England, was convicted of treason and beheaded in Salisbury on 2 November 1483, in fact before Henry's ships made landfall. Henry's conspiracy against Richard III had unravelled, and without Buckingham or Henry, the rebellion was easily crushed.
Survivors of the failed uprising then fled to Brittany, where they openly supported Henry's claim to the throne. On Christmas Day in 1483 at Rennes Cathedral, Henry Tudor swore an oath to marry Edward IV's daughter, Elizabeth of York, and thus unite the warring houses of York and Lancaster. Henry's rising prominence made him a great threat to Richard III, and the Yorkist king made several overtures to Francis II to surrender the young Lancastrian. Francis II refused, holding out for the possibility of better terms from Richard. In mid-1484, Francis was incapacitated by illness and while recuperating, his treasurer, Pierre Landais, took over the reins of government. Landais reached an agreement with Richard III to send Henry and his uncle back to England in exchange for military and financial aid. John Morton, a bishop of Flanders, learned of the scheme and warned the Tudors; the Tudors then fled to France. The French court allowed them to stay and provided resources. For the French, the Tudors were useful pawns to ensure that Richard's England did not interfere with French plans to annex Brittany. Thus the loss of the Lancastrians seriously played against the interests of Francis II.