His great - grandson , the fourth Baron , was made Earl of Ardglass in 1645 .
The final creation of the title came in 1540 for Cromwell 's son , Gregory , also by letters patent .
Cromwell 's great - grandson , the fourth Baron , was made Earl of Ardglass in 1645 .
The final creation of the title came in 1540 for Cromwell 's son , Gregory , also by letters patent .