A court has ordered Austria to return five paintings by Gustav Klimt to the heir of a Jewish family that fled the country during the Nazi era.
A portrait of Mrs Altmann's aunt is among Klimt's most famous works
The paintings, which are worth at least $100m (£59.6m), have been the subject of a legal battle between Austria and the heir, Maria Altmann, since 1998.
The Austrian government has not yet commented on the decision to return the Klimt paintings.
But a lawyer for Mrs Altmann told the BBC the ruling was binding and final.
Art Nouveau master Klimt is one of Austria's most celebrated painters. The paintings include one of his most famous works, a portrait of Mrs Altmann's aunt, Adele Bloch-Bauer.
When Adele died in 1925, she left a will asking her husband, Ferdinand Bloch-Bauer, to leave the works to the Austrian Gallery upon his death.
But when the Nazis took over Austria in 1938, Mr Bloch-Bauer and his niece were forced to flee for their lives.
The paintings were seized and put on display in a Vienna museum where they remain to this day.
There has been a long legal battle over ownership of the paintings, which went all the way to the US Supreme Court.
The decision by the arbitration court in Vienna now paves the way for one of the largest post-war restitution settlements in Austria.
In April 2005, Mrs Altmann was part of a group which received $21.9m (£11.9m) from a Swiss bank fund set up to compensate heirs of Nazi victims.
Her family, major shareholders in an Austrian sugar refinery before World War II, had their savings plundered from a Swiss bank by the Nazis.