The Treaty of Brussels was an agreement between representatives of Philip IV of Spain and Charles II, the leader of the exiled royalists of England, Ireland, and Scotland.
1656 for Charles II by James Butler, 1st Marquess of Ormond (who later became duke) and Henry Wilmot, 1st Earl of Rochester.
In exchange for future Spanish military support for a potential restoration, Charles agreed to raise forces to fight for Spain in the ongoing Franco-Spanish War (1635–1659).
[6] Large numbers of Irish troops deserted from the French army to serve under the Duke of York in the hope that they could invade England.
Spain then made peace with France at the Treaty of the Pyrenees in 1659, and even the death of Oliver Cromwell the previous year did not lead to the immediate collapse of the Commonwealth.
The failure of Spain, however, to assist Charles' return to London meant that he did not feel bound by the treaty and so he annulled it.