After seeking Spanish support late in 1638 for action against the Regent
Christine of Savoy,
Madame Royale, Thomas went to
Milan early in 1639, and alongside Spanish forces invaded
Piedmont, where many towns welcomed him. He took Turin by knavery but the French continued to control its citadel. In 1640, he held the city in the multi-layered
siege of Turin. After repeated bouts of negotiations with the Regent and the French, Thomas Francis made peace with both in the first half of 1642, unblushingly changed sides, and started fighting with the French against the Spaniards.
Service with France For the rest of 1642 and part of the 1643 campaigns, Thomas Francis commanded Savoyard forces fighting alongside the French under
Henri II d'Orléans, duc de Longueville, against the Spanish, generally along the Piedmont–Milan border; when Longueville was recalled home, he succeeded him as allied commander-in-chief, with
Henri de la Tour d'Auvergne, Vicomte de Turenne, as his second-in-command. Thomas Francis was given the supreme command only because of his birth; another French general,
César de Choiseul du Plessis Praslin, observed a few years later that French marshals would only serve under someone who was superior to them in social rank, and Thomas Francis, with his blood relationship to the French and Spanish royal families, was the only candidate. By late summer, both Thomas Francis and Turenne were seriously ill and du Plessis Praslin was in temporary command. Thomas Francis led the joint armies again in 1644, taking Santya and
Asti; he also tried to take
Finale Ligure but gave up the attempt, apparently because he feared this valuable port would end up under French control rather than Savoyard. In 1645, now commanding with du Plessis Praslin, he took
Vigevano, and repulsed a Spanish attempt to block his withdrawal at the River Mora, the nearest he ever came to a success in the field. In 1646, Thomas Francis was put in command of the French expedition sent south to take the Tuscan
forts, after which he was to advance further south to Naples, drive out the Spanish and put himself on the throne of the
kingdom; but the expedition set off late, and when he
besieged Orbetello, the supporting French fleet was defeated by the Spanish and he was forced to raise the siege and conduct a difficult retreat, which he performed poorly. In the 1647 campaign, Thomas Francis is mentioned as commanding alongside the French general in the forces sent across north Italy to work with the Duke of Modena
Francesco I d'Este who had just allied with France and opened up a 'second front' against the Spaniards in
Milan, though Mazarin confessed that he had appointed Thomas only because he feared that, if left behind in Piedmont, the Prince's
restless spirit would make more trouble. In January 1654, when the last of the ceremonial offices formerly belonging to the rebel leader
Louis II de Bourbon, Prince de Condé, were disposed of, Prince Thomas Francis was made
Grand Maitre. The Franco-Spanish war had been continuing in north Italy, and late in 1654 the increasing Savoyard hostility to the current French commander Grancey led to a search for a new allied commander-in-chief; the French would have preferred to send the
Duke of York (later
King James II); as he was unacceptable to Turin, Thomas Francis was appointed as joint commander, akthough his wife was held in France almost as a hostage for his good behaviour. On 16 December 1654, he arrived in Turin to a ceremonial welcome by the French troops and an unexpectedly friendly reception by Duke
Charles Emmanuel. After the 1655 campaign, Thomas Francis returned to Turin where he died the following January. ==Second generation==