Behind the scenes
This timeless gold ring contains green amber collected by the Doctor on the planet Raxacoricofallapatorius. It reminds him of all the wars he has won but also all the lives he has taken. This thought lurks on his conscience to this day. To Peter, Best wishes being the New Doctor Who from Idris (11)
The ring was, in actuality, two bands, which comprised of Peter Capaldi's own wedding ring, and a separate band with the green stone, which backed up against Capaldi's own ring. This was done so Capaldi would not have to remove his ring during filming. In the final scenes of TV: Twice Upon a Time, when the ring fell off the Thirteenth Doctor's finger, Jodie Whittaker was only wearing the secondary band for the shot.