The 1973 episode of Doctor Who, The Three Doctors, was William Hartnell's last appearance as the First Doctor. As Hartnell was in poor health, plus suffering from Alzheimer's, he was, therefore, reduced to a pre-recorded cameo role, appearing only on the TARDIS's scanner and the space-time viewer of the Time Lords. Hartnell's scenes were filmed at BBC's Ealing Studios, where he would sit down during the shoot and read his lines from cue cards. It would be the last time Hartnell played the Doctor and his last acting role ever before his death in April 1975.