After the Seven Years War Frederick the Great held quite a bit of animosity toward England. He felt he had been abandoned by his former ally when they made peace with France. But he also had no wish to provoke England. His writings from 1765 to 1778 reflect a desire to help the colonists only because it would hurt England. But his mood seems to shift and he does show some fondness for the Colonies toward the end of his life. At one point he limited the movement of mercenaries across Prussia which for a time stopped the Hessian influx of troops to America. He did this for a number of reasons including preserving Prussian manpower and stopping problems caused by the mercenaries as they travelled. However, his writing indicate he took special delight in the measure also hurting the English.

Throughout the revolution he was friendly with the colonist's ambassador but he never provided direct help because he didn't want to risk a war with England. He sympathized with the Colonists as he felt the English were "Brutish" in their laws. As things progressed he does seem to develop a genuine fondness for the colonies that extended beyond just his desire to see the British get bloodied.

And of course Prussia was the first European Power to recognize The United States with the Treaty of Amity and Commerce. Again in this his writings indicate both a fondness for the Colonies and a desire to stick it to the British.

There is a wonderful write up of it in The American Historical Review