The fourth baronet married Lady Henrietta Somerset, fifth daughter of the fourth Duke of Beaufort, a man of Jacobite sympathies who was reputed to have sheltered Sir Watkin 3rd Bart after the collapse of the Jacobite rebellion in 1745. Sir Joshua Reynolds painted the betrothal portrait of the young couple. They were married in April 1769 and Henrietta died on 24 July.
A monument to her memory by Joseph Nollekens was erected in the centre of the north chapel in 1773; it is now at the west end of the north aisle. The figure is placed upon a pedestal in the shape of a Roman altar and the Lady is shown resting one hand on an urn which represents mortality and the other on an anchor (hope), and there is a serpent with its tail in its mouth symbolizing eternity .The monument cost £450. Sir Watkin named his second daughter Henrietta (b.1780).