During the Fronde, Thomas linked himself closely with Cardinal Mazarin, who, although effectively prime minister of France, was like him an Italian outsider at the French court. In the early 1650s, Thomas was seen as an important member of Mazarin's party, closely linked to the Cardinal, regularly seen in conference with him, and active in his support. In 1651 when Mazarin had been forced into exile, the Prince was for a time brought onto the conseil du roi, and an (admittedly very hostile) contemporary the duchesse de Nemours described him as a 'prime minister without being aware of it'; there were suggestions that Mazarin's opponents within the court had raised him up as a rival to the cardinal with the Queen, but this is unlikely, especially since Mazarin himself urged the Queen to follow Thomas' advice, and it is more probable that Mazarin backed the Prince as someone who would keep other rivals from gaining control in his absence but who would never have the status within France to set himself up as a permanent replacement for the Cardinal. By the time Mazarin returned from his second and last exile in February 1653, Thomas, who accompanied the court to St Denis to welcome the Cardinal home, was insignificant again - an analysis of Mazarin's close colleagues at this time by the later historian Chéruel made no mention of him. 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 was made Grand Maitre.