From Ancestry's Irish Records Extraction Database:
Name: George Mostyn
Sex: Male
Marriage: 09 October 1734
Marriage Place: St. Mary, Dublin, County Dublin, Ireland
Spouse: Barbara Ross
Miscellaneous: Prerogative court license
Source: A. E. Langman. Marriage Entries in the Registers of the Parishes of S. Marie, S. Luke, S. Catherine, and S. Werburgh, 1627-1800. Exeter & London: William Pollard & Co. Ltd., 1915. 143 pages.

Here lieth the body of Barbara Mostyn
who Depd this life 28th Novr 1789 aged 80 yrs
also the Body of Mr George Mostyn
who Depd this life 6th June 1791 aged 83 yrs
also William Mostyn who Depd
this life the 19th of July 1811 Aged
65 years