Mark Gatiss holds the record as the Doctor Who writer with the most acting TV roles in the show. His appearance as British First World War soldier "The Captain" (whose identity we have some ideas about) in this year's Christmas special will make it four characters across five episodes.
But he's not the only person to have penned episodes of Doctor Who and appeared in it – in fact, he's not the only writer in the Christmas special...
Appearing opposite Gatiss – quite literally – in the trailer for Twice Upon a Time is none other than Toby Whithouse, the man behind no less than seven episodes, including series two's School Reunion, series six's The God Complex and series nine two-parter Under the Lake/Before the Flood.
You can get a closer look at him as a German officer in the main image above – and here he is in a much more flattering image for comparison.
As yet, we don't exactly what's happening during Gatiss and Whithouse's encounter but in the trailer they appear to be frozen as Peter Capaldi's Twelfth Doctor tells us "something has gone very wrong with time – we're trapped inside a single moment".
They're also pointing their guns directly at one another. So perhaps there's a bit of rivalry between Doctor Who writers...
The Doctor Who Christmas special Twice Upon a Time is on BBC1 this Christmas