Christie's auction house said Monday it will sell about $30 million worth of artifacts from Althorp House, in Northamptonshire, central England.
Althorp is the home of Diana's brother Earl Charles Spencer, who recently announced his engagement to Lady Bianca Eliot.
The Rubens portrait "Commander Being Armed for Battle" has been owned by the Spencer family since 1802.
Other lots include a painting by Giovanni Francesco Barbieri and 19th-century horse-drawn carriages.
Three auctions will take place during the summer.