OK, have we all worked out our issues with Matthew Crawley/Dan Stevens and are moving on bravely to Season 4? (Those who are fed up with the show and aren’t watching it any more — well, you’re not bothering to read this post, are you?) Here’s some casting news for the upcoming season, which is currently shooting — and, yes, spoiler alert if you don’t want to know. (But if you don’t, why are you reading?) By now many of you may have heard that O’Brien is scuttling off into the sunset: Siobhan Finneran, who plays scheming lady’s maid O’Brien, is leaving the show — however, unlike Matthew and Sibyl, the character isn’t being killed off so the door’s open for a possible return. (My book group discussed this yesterday and concluded that she got a job offer from Shrimpy’s wife. And that the new interest in “her ladyship’s soap” may have inspired her to clear out of Downton.) On the plus side of things: Shirley MacLaine is returning as mother-in-law-from-hell Cora Levinson, and several new faces are joining the cast. Opera singer Kiri te Kanewa (maybe she’s a ‘Downton’ fan?) will appear as “a guest who sings in the house” and the great Harriet Walter, who’s been in loads of things but to me will always be the sneering sister-in-law in “Sense and Sensibility,” has been cast as Lady Shackleton, a posh friend of the Dowager Countess. (“I am exceedingly fond of a cottage. A cottage is always very snug.” ) Also new: Tom Cullen, who will play a family friend, Nigel Harman as a new valet, and Joanne David as the Duchess of Yeovil.