It’s the House of Saud’s worse nightmare come true. The stunning success of the Zaydi Houthi rebellion in Yemen places a Shiite group with connections to Iran on the soft underbelly of the Kingdom of Saudi Arabia, erasing years of Saudi efforts to stabilize Yemen and keep it in the Saudi orbit.

The Zaydi Houthi movement, which calls itself Ansar Allah, took control of the capital, Sanaa, in September and now has taken control of the main northern port of the country at Hodeida. The Houthis have expanded far beyond their traditional stronghold in the north of Yemen around Saada near the Saudi border to take control of much of northern Yemen. They are dictating who and what they will accept in the nominal government of Yemen. They rejected President Abed Rabbo Mansour Hadi’s first choice for a new prime minister, and rejected his requests that they evacuate Sanaa and return to their bases in the north.

Named after the founder of the modern Zaydi movement, Hussein Badreddin al-Houthi, who was killed in the first of six wars between 2004 and 2010 waged by the rebels against the Sanaa regime, the Houthis are now the dominant military force in the country. The Zaydis are an offshoot of Shiite Islam, which controlled North Yemen until the 1962 revolution. The Zaydi Imamate was toppled by an Egyptian-backed nationalist movement and retreated into the rugged mountains and deserts of the north to wage a six-year insurgency against the Egyptians and their Yemeni republican allies. The Saudis were the major source of outside support for the royal rebels. King Faisal was their primary advocate.

So it is deeply ironic that today the Saudis are so alarmed at the Zaydi takeover of Sanaa and Hodeida. Before the Arab Spring came to Yemen in 2011 the Saudis supported then-Yemeni President Ali Abdullah Saleh’s military campaigns against the Houthis and fought a series of their own military campaigns against them along the border after 2009. The Saudi army and air force were not particularly effective in these operations, so any residual Saudi-Zaydi affection was long gone by the time Saleh was ousted and his deputy Hadi took charge of Yemen.