Matt smith originally auditioned for the role of sherlock in the BBC show, but Benedict cumberbatch was chosen over him. But Steven liked his acting so much he promised him a role in one of his shows. That show was doctor who.
The BBC, ladies and gentlemen.<-- Am I the only one that thinks, if there is ever a special where this happens, that Peter NEEDS to play old Sherlock! But I would love the Doctor to meet Sherlock<---they need to make a SuperWhoLock TV show
The only time Sherlock lost it in this episode was when he thought John was doubting him. :( please excuse that sound, it's the sound of my heart ripping to shreds and my johnlock feels exploding and sobs erupting from my eyes