The king's approval ratings have fallen nearly 35 percentage points in two years. BALLESTEROS/AFP/Getty Images

Almost two-thirds of Spaniards want their king to abdicate and hand the crown to his son, according to a poll released on Sunday, the monarch's 76th birthday.

King Juan Carlos, who has been on the throne for 38 years, was once one of the world's best-loved sovereigns, respected for his common touch and for helping guide Spain to democracy in the 1970s following the death of dictator Francisco Franco.

But Spaniards have become increasingly frustrated by a long-running corruption investigation into the king's youngest daughter, Princess Cristina, and her husband former Olympic handball player Inaki Urdangarin — particularly at a time of economic crisis and widespread unemployment.

Urdangarin has been charged with embezzling 6 million euros in public funds, though both deny any wrongdoing.

The king's approval rating also took a big hit in April 2012 when he fell and broke his hip during an elephant-hunting safari in Botswana, a lavish privately funded trip that was secret until his accident — and came at a time of particularly harsh public spending cuts.

Sixty-two percent of those interviewed by pollster Sigma Dos for Spanish newspaper El Mundo said they thought the king should step down, compared with 44.7 percent a year ago.

Only 41.3 percent of those polled had a good or very good opinion of the king, down from more than 76 percent two years ago.

Younger Spaniards, who were not alive during the Franco years, were overwhelmingly in favor of abdication, the poll showed.

General support for the monarchy as an institution, however, fell below half to 49.9 percent, according to the poll.

A majority however support his son and heir Felipe and believe he could restore the family's prestige, according to the study.

A series of hip and back operations and other health problems have fueled speculation the king might abdicate, but in his annual Christmas Eve speech, he reiterated that he was not contemplating such a move.

The telephone poll of 1,000 adults was carried out between Dec. 28 and 31.

Wire services