Christina, younger daughter of Christian II of Denmark and Isabella of Austria, sister of Charles V, was born in 1522. In 1533 she married by proxy the Duke of Milan, who died in 1535.
Holbein visited Brussels in 1538, and for three hours Christina sat for a portrait. She wears mourning clothes. The English ambassador was arranging for Henry VIII to see the Duchess's likeness in connection with plans to marry her.
However, in 1541 she married François, Duc de Bar, who succeeded his father as Duc de Lorraine in 1544 and died in 1545, leaving Christina Regent of Lorraine. She died in 1590.
From The National Gallery Podcast: Episode Twenty Six, December 2008