Princess Diana's Brother Earl Spencer Debuts The Sequel To His Historical Bestseller 

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Charles Spencer is a part of royal history himself — and he’s also an expert on the kings and queens of the past.

To Catch A King: Charles II’s Great Escape,

debuts this week and is a follow-up to his 2015 bestseller

The book was celebrated at an event in London on Thursday at the Ralph Lauren store on fashionable Bond Street. (The location was fitting: Charles II

A wonderful evening celebrating the launch of #ToCatchAKing now exclusively available to purchase from Ralph Lauren New Bond St until Oct 5! pic.twitter.com/ezl0IK5SeE

— CharlesSpencer Books (@cspencerbooks_) September 29, 2017

The 9th Earl Spencer noted that the monarch once bought 10 purple capes and purchased as many as 40 suits in one year. At one point, Spencer said, Charles II spent 1 percent of the nation’s wealth on himself in a single year. (Really.)

Charles II was on the throne during one of the most revolutionary periods in British history: 

tells the story of the search for the monarch, who was on the run after he was defeated by the armies of Oliver Cromwell.

The king’s flight lasted over six weeks throughout England. He famously stayed in an oak tree and in country homes of allies, which is captured in all its gripping adventure in the book.

Watch @BBCLookEast this evening to see a fun report on King Charles I's visits to @AlthorpEstate in the #17thcentury pic.twitter.com/zV1E0oQSDm

— Charles Spencer (@cspencer1508) September 29, 2017

is Spencer’s sixth book. His previous works cover the execution of Charles I, a biography of Prince Rupert and the story behind his family’s ancestral home, Althorp. Of course, as well as writing, he heads up the family estate, where his sister Princess Diana is laid to rest.

As he finished writing the book earlier this year, Spencer also marked the 20

anniversary of Diana’s death. He spoke to PEOPLE and ABC about her legacy for the documentary

Spencer was joined at the book launch by his wife, Karen Spencer, who is the founder and CEO of Whole Child International, his sister Lady Sarah McCorquodale, British Foreign Secretary Boris Johnson, actress Joan Collins and historian Kate Williams.

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