House of Forbes branches, or cadet houses, have descended from younger sons of the various Lords Forbes. For example, from Duncan, second son of James, 2nd Lord Forbes, descended the houses of Corsindae, Balfluig, Monymusk, Leslie, and others. From his third son, Patrick, came those of Corse, Craigievar, Granard, and others.
The second son of Duncan Forbes of Corsindae founded a family which almost rivalled that of his elder brother in importance -- and lasted longer. Like his father, he was named Duncan. Both he and his father advanced large sums on the Priory lands of Monymusk, having a charter from Pope Julius III to “set the Mains of Monymusk.” In 1560, he foreclosed the mortgages and came into possession of the Monymusk Estate from the Frasers.
Duncan Forbes, now the first Laird Monymusk, had three sons and three daughters with his wife Agnes Grey, daughter of a fellow Baillie of Aberdeen. Duncan and his wife both died in 1584. In 1589, his eldest son and heir William obtained a Crown Charter erecting the town and lands of Monymusk into a borough of barony. His heir, also named William, bought additional land and was created a baronet by Charles I in 1626 -- among the earliest in Scotland.
During the Scottish Civil War between the Covenanters and Royalists, Sir William, 4th Laird and 2nd Baronet, joined Covenanter Archibald Campbell, the Marquis of Argyll, at Dunnottar Castle in April, 1644. James Graham, 1st Marquess of Montrose initially joined the Covenanters in war but subsequently became a Royalist in support of King Charles I. Montrose marched on Monymusk when Sir William was still in the field – but spared the estate due to the hospitality of Sir William’s wife Jean Burnett of Leys. As 17th century historian John Spalding relates, “the Marquis dynit at Monymusk with the lady, the laird being absent, and upone fair conditiones, he spairit him at this time.”
Unfortunately, his grandson, Sir William, the 4th Bart. of Monymusk, was not likewise able to save the Monymusk Estate. In 1712, he became bankrupt and sold Monymusk to Sir Francis Grant, Lord Cullen, for £96,000 Scots (£9,600 sterling). Even without land, the Forbes of Monymusk eventually thrived once more.
Sir William, 5th Baronet of Monymusk, was born in 1707 and succeeded his grandfather in the title at the age of eight since his father John had died. His mother Mary (daughter of Alexander Forbes, 3rd Lord Forbes of Pitsligo) then remarried James Forbes, afterwards 15th Lord Forbes. William became an advocate in 1727, and in 1741 was elected Professor of Civil Law in Aberdeen.
Through his grandmother Mary, the 7th Baronet Sir William was styled Forbes of Monymusk and Pitsligo. He married Williamina Belches Stuart and his son was John Stuart Hepburn Forbes, 8th Baronet of Monymusk, of Fettercairn and Pitsligo. This House of Forbes branch has continued to this day as Stuart-Forbes of Monymusk.