Question: Who is the paternal grandfather of Pierce Somerset Butler?
Answer: Edmund Butler, 11th Viscount Mountgarret

"Verdict for plaintiff who thus came into a peerage, defendant being proved illegitimate" Pierce Butler (6 May 1774 – 18 August 1846) was an Irish politician in the United Kingdom House of Commons. Butler was the son of Edmund Butler, 11th Viscount Mountgarret and Lady Henrietta Butler. He married Anne March, daughter of Thomas March, in 1800