Hon. Harold Plantagenet Mostyn was the son of Major Hon. George Charles Mostyn and Mary Monk; his elder brother was the 7th Baron Vaux of Harrowden. One sister was the sculptress Lady Rivers Wilson.
Lady Archibald Campbell interceded with JW on his behalf in 1899, asking JW to admit one of Mostyn's paintings to the exhibition of the International Society of Sculptors, Painters and Gravers (#00523).
He is referred to in JW's correspondence about 1899.
http://www.thepeerage.com (accessed 2004).