Alexander Forbes (ca. 1464 – 1491), succeeded his father William “Grey Willie” Forbes as the 4th Lord Forbes in 1483. To secure the loyalty of the Forbeses, the Scottish King James III agreed to the marriage between Forbes and his niece Margaret Boyd, the only daughter of Thomas, Earl of Arran, and of Princess Mary, his sister. The handwritten chronicle which provided the primary source for Matthew Lumsden’s "Memoirs of the House of Forbes or a Particular and Exact Genealogie of that Ancient and Honourable Surname" of 1580, notes that “Alexander, the 4th Lord Forbes and second of that name was one of the greatest Hectors of his age.” His battle skills were tested during the Scottish civil war of the late 15th century.
In 1474, James III arranged for his heir James (later James IV) to marry the English princess Cecily of York, daughter of Edward IV of England. This alienated many members of his own family and the Scottish nobility. As a result, James III faced major rebellions during his reign. The King failed to make dowry payments and England once again invaded Scotland in 1482, led by Cecily’s uncle Richard, Duke of Gloucester, and the James III’s younger brother, Alexander Stewart, Duke of Albany. He beat back the English forces but was later abandoned by many of the Scottish lords.
However, Forbes remained loyal to the King. Scottish poet William Drummond Hawthornden (1585 –1649) wrote “When in the year 1488 the majority of the Nobles rose in arms against their King, finding in the north most loyal, the King went thither and levied a considerable army there, held Justice Courts at Aberdeen and Inverness, preparing and modelling his forces to the best advantage. Where among others of the loyal nobility who were flocking to him dayly, Alexander, Lord Forbes, being now in the vigour of his youth <probably about 25 years of age>, with a gallant company of his friends, allys and vassalls, offers his services, whom the King received with a particular respect, establishing him as Lieutenant in those northern districts beyond the Grampians – the Earls of Huntley being of the contrary faction.” Walter Macfarlane's "Genealogical History" (1750-1751) also noted that the James III granted the “whole ruling and guiding of the King's affairs” in the district between Forfar (in Angus-shire) and Caithness-shire to Forbes.
Therefore, Forbes fought on behalf of his King against the rebellious Scottish lords, led by the King’s son, at the Battle of Sauchieburn on June 11, 1488. When James III was killed in the battle, Lord Forbes rode throughout northern Scotland carrying the King's bloody shirt on his spear and attempted to rouse an army to avenge him. He succeeded in getting together a large force but he laid down his arms after the defeat of the Earl of Lennox at Tillymoor, near Stirling. The young James IV pardoned Forbes and allowed the Lords Forbes administration of northern Scotland until about 1500.