Portrait of 17th century royal mistress on sale

LONDON (Reuters) - A 17th century portrait by Dutch-born painter Peter Lely of a semi-naked English royal mistress goes on sale in July with a price tag of up to two million pounds ($4 million).

Painted for Charles II in the hedonistic days of the English Restoration after years of Puritanical rule, the painting depicts a slim young woman lounging against pillows with only a sheet draped lightly across her thighs to preserve her modesty.

Hanging in the royal bedchamber behind a secret sliding panel to keep it from prying eyes, the painting was initially catalogued in 1688 as a portrait of famed royal mistress Nell Gwyn.

But there has always been some doubt that this was accurate, with many experts believing that it is in fact a portrait of Barbara Villiers, Countess of Castelmaine, an earlier favorite mistress of the notoriously philandering king.

"The scales are tipping in favor of it being Barbara Villiers because of the eyes and the hair color and the date it was painted," said a spokesman for auction house Christie's which will put the painting on sale on July 5.

Villiers, who was considered one of the most beautiful Royalist women of the era, became mistress to Charles in 1660 aged 20 even though she was married, and rose to wield immense power in the royal court.

The king later acknowledged that five of her six children were his.

But her extravagance and open promiscuity led to her downfall, and Charles eventually dumped her in around 1673 in favor of Gwyn.

Villiers died in 1709 after suffering from dropsy, an intestinal disease now known as oedema.