Ovenden has been cast as aristocrat Charles Blake. Also joining the series are Tom Cullen as Lord Gillingham, an old family friend of the Crawleys who visits the family as a guest for a house party; Nigel Harman as Green, a valet; Dame Harriet Walter as Lady Shackleton, an old friend of the Dowager; Joanne David in a guest role as the Duchess of Yeovil; and Dame Kiri Te Kanawa as a guest who sings in the house.

"The addition of these characters can only mean more delicious drama — which is what 'Downton Abbey' is all about," said Masterpiece executive producer Rebecca Eaton in a statement.

Actress Shirley MacLaine (The Pajama Game, Me and Juliet) will also return to the show for next season's finale. She will reprise her role as Martha Levinson.