The headstone does have the date of death as 1869.(Was there more than one Thompson F Westbrooks?)
However, records show that Thompson F Westbrook died 25 Jul 1863 after being wounded in the battle at Vicksburg.This death date is consistent with his widow marrying James Madison King in April 1866.
From Ancestry.com: Name: Thomas F Westbrook Residence: Forsyth County, Georgia Enlistment Date: 5 Jun 1862 Rank at enlistment: Private State Served: Georgia Survived the War?: No Service Record: Enlisted in Company I, Georgia 43rd Infantry Regiment on 06 May 1862. Mustered out on 25 Jul 1863 at Vicksburg, MS. Sources: Roster of Confederate Soldiers of Georgia 1861-1865