Through his ancestor Edmund MacRichard Butler, Peter is related to the Polestown cadet branch of the family.
Edmund MacRichard Butler's eldest son, Sir James Butler headed up the Polestown house.
This line would go on to produce a series of Earls and Dukes of Ormond.
The second son of "The MacRichard", Walter, would go on to produce this "Roscrea" cadet line as well as the minor nobility of Baronets Polestown.
Peter's grand-nephew Sir Walter was the 1st Baronet.