Having made the discovery that several Royal fishings in the province of Ulster belonged to the Crown, he petitioned the king and an inquiry was thereupon instituted.
Sir Arthur was eventually rewarded by a grant of such proportion of the said fisheries as he thought proper to demand, besides the sum of £3000 from the profits of the remainder.
He had previously obtained extensive territorial possessions from the crown, particularly a grant of various lands in County Longford, in all 1,266 acres (5.12 km2), which were erected into the manor of Castle Forbes, with the usual manorial privileges.
A lieutenant-colonel, he had accompanied his regiment to assist King Gustavus Adolphus of Sweden, but was killed by Frederick Hamilton in a duel at Hamburg in 1632.
[2] Forbes married after February 1618, Janet (d. after Sept 1642), daughter of Maurice Lauder of Belhaven and West Barns (d. 1602), Member of Parliament for and Baillie and Burgess of, Dunbar, by his third wife Alison Cass.