Prince Alwaleed bin Talal, the pugnacious Saudi Prince worth billions, is suing Forbes magazine for allegedly undervaluing his wealth by $9.6 billion.

One of the richest and most influential businessmen in the Middle East, Alwaleed cut ties with Forbes in March after the magazine placed him as the 26th most wealthy billionaire on its annual Rich List, valuing him at $20 billion.

The prince claimed he was worth closer to $30 billion and, through his chief financial officer Shadi Sanbar, trashed the magazine, saying it was full of “sensational dirt-digging and rumor-filled stories.”

Alwaleed, known for his opulence and obsession with image, has now filed a defamation claim against the magazine in a high court in London, according to the Guardian.

Kerry A. Dolan, the 19-year veteran at Forbes who wrote the story, said the value of Alwaleed’s Kingdom Holding was estimated by the underlying value, not solely the price of its shares on the Saudi stock exchange.

“We took the value of the equity as spelled out in the 2012 year-end financials and appreciated it to include gains in share prices through Feb. 14, the day we used to value everyone’s net worth,” she wrote in a post, responding to CNBC’s questioning of her calculations. “We took account of the real estate owned by Kingdom Holding as well, using the company’s year-end 2012 financials as a guide.”

A Forbes spokeswoman did not immediately respond to emails and calls requesting comment, but said in a statement to the Guardian: “We’re very surprised at claims that Prince Alwaleed has decided to sue Forbes, particularly if he has done so in the United Kingdom, a jurisdiction that has nothing whatsoever to do with our recent story which raised questions about his wealth.”

Until recently, London had been a destination for “libel tourism,” where publications were long likely to lose libel lawsuits. But recent legislation aimed at curbing the bias toward litigants in such suits was passed in April.

“The Prince’s suit would be precisely the kind of libel tourism that the U.K.’s recently-passed libel reform law is intended to thwart,” Forbes said in the statement. “We would anticipate that the London high court will agree. Forbes stands by its story.”

A spokesman for Kingdom Holding did not immediately respond to an email requesting comment.