Kathmandu, Nov 18 (IANS) Nepal Police Wednesday said they have begun investigating the backgrounds of a pair of lovers who tried to extort former Nepal king Gyanendra's daughter Prerana Singh.

'We have handed over the couple to the crime investigations department,' said Deputy Superintendent Pradyumna Karki. 'They will remain in police custody for 25 days while investigations are completed.'

The capital was agog Wednesday after the news broke that the deposed king's daughter, who was married to a commoner businessman, had been receiving threatening messages on her private cell phone, asking her to pay up NRS 10 million or face the abduction and killing of her husband and school-going son.

Karki said the sender of the messages, a man in his 30s, was arrested from Nepalgunj town on the India-Nepal border Tuesday after the former princess' husband Raj Bahadur Singh lodged a formal complaint with police.

The arrested man, Rajesh Hamal, reportedly told police that he was a supplier of the wonder herb yarshagumba, known as Nepal's Viagra, and had suffered a hefty loss in business recently.

Hamal also reportedly told police his girlfriend, Preksha Shah, was the former princess' secretary and it was she who had provided the phone number to him.

Karki said Preksha had also been arrested and police would charge them both with attempted abduction and trafficking.

This is the first time that Nepal's former royal family has featured in a police case.

However, Karki said that the former princess or her husband may not have to appear in court during the trial unless the judges specifically ask them to be present.

Till last year, when Nepal's newly elected lawmakers voted overwhelmingly to abolish monarchy, Nepal's royal family were regarded to be above law by the constitution.

Though Prerana's brother and former crown prince Paras is alleged to have run over a popular singer, causing his death, no action could be taken against him.