"Balthazar (Salty) married Anne Maria de Burgh, the illegitimate daughter of Lord Clanricarde at Beaulieu on 7th March 1793,"
https://beaulieuhistorysociety.org.uk/images/newsletters/BHSNewslet...
There is a baptism record for "Ann Maria Deburgh" in 1770 in St George, Hanover Square that lists 'John' and 'Mary' as the parents.