Question: Who is the mother-in-law of Lady Brigid Guinness?
Sentence (from "Prince Frederick of Prussia (1911–1966)"): Prince Frederick of Prussia (19 December 1911 – 20 April 1966), also known as "Mr. Friedrich von Preussen" in the United Kingdom, was the fourth son of Crown Prince Wilhelm of Germany and Duchess Cecilie of Mecklenburg-Schwerin.
Relevant evidence: Yes