David Tennant and Neil Patrick Harris were spotted filming the Doctor Who 60th Anniversary in the streets of Bristol.
It was announced earlier this week that the How I Met Your Mother actor would be joining forces with Tennant and a host of other returning actors for the special episode.
Catherine Tate will be reprising her role as Donna Noble, and it's thought Bernard Cribbins will also return as Donna's grandfather Wilfred Mott.
