The Hour star Romola Garai will play a nurse guiding an ailing Winston Churchill back to health in a new drama about his final years in power.
She will star alongside Michael Gambon, who plays the prime minister, in the one-off film Churchill's Secret which is being filmed at his country home of Chartwell in Kent.
The cast, which also includes Matthew Macfadyen, Downton Abbey's Daisy Lewis and Tara Fitzgerald playing his adult children, started filming this month.
The show, which will also be broadcast on PBS in the United States next year, is set during the summer of 1953 when the then-peacetime prime minister had a stroke, which was kept secret from the world.
The previously announced Lindsay Duncan, who plays his wife Clementine, is joined in the cast by Bill Paterson and James Wilby who play two of his closest advisers .
ITV director of drama Steve November said: "Churchill's Secret is the extraordinary and compelling story of how one of our country's most famous political figures battled back from life-threatening illness to hold on to power.
"We're delighted to commission Churchill's Secret from Daybreak Pictures and to be working with Michael Gambon as Sir Winston Churchill and Lindsay Duncan as his wife Clemmie."