LONDON (REUTERS).- A painting by Flemish master Peter Paul Rubens, put up for auction by the aristocratic family of the late Princess Diana as part of a clearout sale, sold on Tuesday for 9 million pounds ($13.68 million).

The picture "A Commander being armed for Battle," was painted in 1613 or 1614, and Christie's, which sold the work as part of its Old Masters auction in London, described it as one of the most important Rubens still in private British hands.

The bearded man gazing toward the viewer has been named by some experts as Emperor Charles V and Christie's had valued the picture at 8-12 million pounds ($12-18 million).

The painting has been at the late princess's ancestral home Althorp for more than 200 years, and was originally described as the "school of Rubens" in an 1802 inventory.

Since then it has been recognized as a Rubens original by leading scholars, Christie's said.

Another work by Rubens, "The Massacre of the Innocents," sold for 49.5 million pounds at Sotheby's in London in 2002, a world auction record for an old master.

Also sold by Diana's brother Earl Spencer at the auction was "King David" by Baroque artist Il Guercino, which sold for 5.2 million pounds.

A portrait by Georg Pencz, dated between 1500 and 1550, sold for 5.6 million pounds, an auction record for the artist.

Overall the auction raised 42.3 million pounds versus forecasts of 36.9-55.8 million, and was described by Christie's as "solid."

Also on Tuesday, rival auction house Sotheby's sold a giant silver wine cooler from the early 1700s for 2.5 million pounds, a record for English silver. The item went to a private Asian buyer.

It was part of Sotheby's "Treasures" auction which fetched 14 million pounds, at the top end of expectations.

(Reporting by Mike Collett-White; Editing by Matthew Jones)