26 June 1914: birth of John Bailey, who played the Commander in The Sensorites (1964), Edward Waterfield in The Evil of the Daleks (1967), and Sezom in The Horns of Nimon (1979-80).
ii) broadcast anniversaries
26 June 1965: broadcast of "The Planet of Decision", sixth episode of the story we now call The Chase; first appearance of Peter Purves as Steven, last appearances of Jacqueline Hill as Barbara and William Russell as Ian. The Mechanoids and Daleks destroy each other; the Doctor rescues captured human pilot Steven, and Ian and Barbara return to the 1960s using the Daleks' time machine.
26 June 2010: broadcast of The Big Bang, ending Season Five of New Who. How to summarise it? Multiple time lines, the Tardis explodes ending the Universe, and Amy and Rory leave their wedding reception too travel with the Doctor.
iii) dates specified in canon
26 June 1284: an alien energy entity posing as the Pied Piper kidnaps 130 children from Hamelin in Germany, as mentioned in the 2009 SJA story, The Day of the Clown.
26 June 2010: Rory Williams starts to travel with the Doctor and Amy, returning to Earth for their wedding, despite the end of the universe; after which they start to travel again.
This is the last set of whoniversaries with entries for all three categories, and the last set of daters specified in canon.