Van Dyck moved to England in 1632
A self-portrait by Anthony van Dyck, owned by the same family for nearly 300 years, is expected to fetch up to £3m when it goes to auction.
The artist painted the portrait in 1641 in the final months of his life, which were spent in London.
Another portrait by van Dyck of his great friend Endymion Porter sold in July for just over £2m - an auction record for a van Dyck portrait.
The self-portrait will be part of Sotheby's Old Masters sale in December.
The Fkemish artist, who was born in Antwerp, Belgium, in 1599, moving to Britain in 1632 to become the court painter of King Charles I.
The painting - titled Self Portrait - has been part of a family collection since 1712, and was recently loaned to Tate Britain for its recent Van Dyck and Britain exhibition.
Sotheby's senior specialist in Early British paintings, David Moore-Gwyn, said: "This is, by far and away, the most important portrait by Van Dyck to come to auction in my 35-year career at Sotheby's.
"It is an exceptional painting by one of the most important artists to have worked in Britain.
"We are delighted to be offering collectors the opportunity to acquire such a rare and unparalleled work by an artist who revolutionised the English portrait."
The current auction record for a van Dyck is £3.06m for A Rearing Stallion, set in 2008.