One of President Donald Trump's least favorite Middle East figures, Prince Alwaleed bin Talal, is under arrest. The president, now on a trip to Asia, once had a Twitter war with the Saudi billionaire, but had remained silent about the prince's plight. Until Monday evening, when he tweeted his support of the Saudi crown prince's move to arrest several princes and other officials.

Without naming Alwaleed specifically, Trump tweeted: "I have great confidence in King Salman and the Crown Prince of Saudi Arabia, they know exactly what they are doing...." He then added: "....Some of those they are harshly treating have been 'milking' their country for years!"

Mr. Trump and the Saudi businessman's longstanding feud, which began during the last presidential campaign, carries a special irony because they have a lot in common. Both are flamboyant real estate investors with multiple marriages (four for the prince, three for the president) who obsess over their financial status and have tense relations with establishment elites.

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In Alwaleed's case, his distance from Saudi Arabia's current rulers resulted in his detention over the weekend along with several dozen others, including fellow members of the desert kingdom's royalty. Crown Prince Mohammed bin Salman, the favorite of his father King Salman, ordered the arrests as part of a crackdown on corruption -- although no details have emerged about specific charges of wrongdoing.

According to news reports, Alwaleed, 62, last summer protested when the king named Mohammed, 32, as crown prince. This position means Mohammed is second-in-command of the Saudi government and designated successor to the king. Salman, 81, is expected to step down in the next few years, but the government has denied that.

Saudi watchers portray Mohammed's wide-ranging arrests as an effort to consolidate power. Mr. Trump has forged a close relationship with both the king and the crown prince. The kingdom is an important Arab ally and a bulwark against Iran's ambitions.

Mr. Trump, of course, has built his political career on slamming establishment elites whom his base blames for the US's torpid economic growth in recent years, as well as for other perceived affronts.

Both Prince Alwaleed and Mr. Trump have long sought the media spotlight. In his pre-presidential days, Mr. Trump was a fixture in the media with his TV show "The Apprentice" and his campaign claiming President Barack Obama was not American born. Alwaleed is known for his many, often shrewd, equity investments, such as in Apple (AAPL) and Citigroup (C). So he has been a sought-after talking head on international business and Saudi Arabia's place in it.

The Alwaleed-Trump tiff began in 2015, when candidate Trump called for curbing Muslim travel to the US in a bid to prevent terrorist attacks. Because of that, Alwaleed tweeted that the Republican front-runner was a "disgrace" and should bow out of the race. Mr. Trump responded that the prince was "dopey" and was seeking to "control our US politicians with daddy's money."

At one point, the future president tweeted a photo of Alwaleed alongside Megyn Kelly, then a Fox News correspondent who had clashed with Mr. Trump. It turned out that the image was a fake, and Mr. Trump falsely claimed that Alwaleed was "the co-owner of Fox News." In fact, the prince had a stake in Fox's (FOXA) sibling company, News Corp. (NWS), amounting to about 7 percent. He since has cut it drastically.

Alwaleed has countered Mr. Trump's attacks by pointing out that he helped bail out the New York developer when the highly indebted Trump empire teetered on collapse in the early 1990s. First, the prince bought Mr. Trump's 283-foot yacht for a bargain price of $18 million and with a partner bought out the Plaza, a storied New York hotel, which the Trump Organization owned.

In numerous ways, the two men have a good deal in common, however:

Wealthy backgrounds. Mr. Trump's father, Fred, made a fortune developing residential housing, mainly in the New York City borough of Queens. Donald's ascent in the business world at least initially was aided mightily by his father's connections and financial heft -- which makes his disparaging reference to Alwaleed and his "daddy's money" incongruous.

Alwaleed's father, Prince Talal, was Saudi Arabia's finance minister in the 1960s. Although he went into exile after clashing with the ruling hierarchy, his son benefited from his connections and finances.

Ambitious real estate developers. At one point, Mr. Trump owned three Atlantic City casinos and many trophy buildings, including Trump Tower in Midtown Manhattan. After his financial near-death experience, he has preferred to manage and brand buildings that others own.

The prince owns or has interests in numerous properties worldwide, such as London's Savoy Hotel. His company, Kingdom Holding, with a partner, is constructing the world's tallest building, in Jeddah by the Red Sea.

Obsession with wealth. The two men revel in being billionaires, with a fixation on gaudy display and a zest for defending their status against doubters. Alwaleed once sued Forbes magazine when it wrote that he had finagled his finances to appear richer than he was. The two sides settled their dispute out of court.

Mr. Trump also is litigious on the question of his net worth. When Tim O'Brien, then at The New York Times and now at Bloomberg News, wrote in a book that Mr. Trump wasn't even a billionaire, the mogul sued. His case fizzled when a judge threw it out.

For the record, Forbes lists Alwaleed as the world's 45th richest person, with $18.7 billion, and Mr. Trump at No. 544, with $3.5 billion.