The actress delved into her roots for the upcoming season seven premiere of pal Lisa Kudrow's hit U.S. ancestry series Who Do You Think You Are? and had no idea her family was mired in a 14th century royal scandal.

According to 700-year-old documents Cox uncovered, her 18 times great-grandfather, Thomas Lord Berkeley, was responsible for looking after his king Edward I's father, Henry III.

A financial account, written in Latin and translated to English, suggests the king's father died in prison while Edward was abroad fighting in the Crusades.

"I’m confused," the actress says in a new trailer for Sunday's (05Mar17) episode. "Why isn’t the father of the king the king if he’s still alive?"

She then learns that the father of the king was living in a chamber, asking, "Was that like a prison? He’s being kept prisoner by his son...? My 18 times great-grandfather, Thomas Lord Berkeley, is holding the king’s father prisoner? Well, this is getting juicy."

Cox visits Britain as part of her own crusade to dig up facts about her ancestor, the first Baron of Berkeley, who lived at Berkeley Castle in Gloucestershire, England.

One of Edward's top soldiers, he fought in the Battle of Evesham in 1265, the Battle of Falkirk in 1298, and the Battle of Bannockburn in 1314, where he was captured by the Scots.

This season's Who Do You Think You Are? ancestry hunters also include Jessica Biel, Smokey Robinson, and Liv Tyler.