"The Shepherd's Boy", sometimes known as "Breaking the Wall", is a leitmotif associated with the Twelfth Doctor, composed by Murray Gold. It appears prominently during the Twelfth Doctor's era, especially during moments of determination, most famously during the climactic scene of Heaven Sent, during which the Doctor punches the Azbantium wall.
Other versions of it are also heard during the Doctor's climactic battle with the Cybermen on the Mondasian colony ship in The Doctor Falls and during his regeneration in Twice Upon a Time, as well as a very brief variation heard in the 60th Anniversary episode, The Giggle.
The piece was first officially released as a video clip from the Doctor Who Finale Countdown, a screening of World Enough and Time that featured that episode's score and other pieces of Murray Gold's music performed live by the BBC National Orchestra of Wales conducted by Alastair King.
The theme is in 6/8 time, based on a part of "I Am The Doctor" and "The Majestic Tale (Of a Madman with a Box)" that was first heard in 4/4 time in the track "This Time There's Three of Us" from The Day of the Doctor, while the War, Tenth and Eleventh Doctors devise their plan in the barn.