Spain's King Juan Carlos will have hip surgery, the royal palace said on Friday, in what will be the 75-year-old monarch's eighth operation in just over three years.

The king, who walks with a crutch and has appeared frail in recent months, will undergo surgery on his left hip, a palace spokesman said.

Juan Carlos is widely respected for his role in steering Spain to democracy after the death of longtime dictator General Francisco Franco in 1975.

But over the past two years he has suffered a number of health problems as well as rare scandals, including a corruption scandal implicating his youngest daughter Cristina, whose tax affairs are being investigated by a judge.

The king's son-in-law, Cristina's husband Inaki Urdangarin, has been under investigation since late 2011 for alleged embezzlement.

The king had both hips replaced in three operations last year.

The first of those came after he fell during an elephant-hunting holiday in Botswana.

Sympathy for his injury was overshadowed by popular anger that he made the trip while Spaniards were suffering in a recession.

The king had a benign tumour removed from a lung in May 2010. In 2011 he was given an artificial right knee and had a torn Achilles tendon repaired.

His most recent operation was in March when he underwent back surgery to treat a slipped disc.

The palace scheduled a news conference for 6:00 pm (1600 GMT) on Friday when it was expected to provide more details on the hip operation.

Despite his operations and opinion polls showing his popularity plunged last year, the king insisted in a televised interview in January that he had "energy and hope" to continue ruling.

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