In a blink and you'll miss it moment from the beginning of Suicide Squad, the first clue to who killed Robin in the DC Extended Universe was revealed. In this article, spoilers for Suicide Squad such as that moment are fair game.
During Harley Quinn's introductory sequence, "Accomplice to the murder of Robin" flashed across the screen. Now, the film's director has gone on record to reveal the true murderer of Robin and the subsequent moments which cost him his teeth.
"This is sort of my personal thing and maybe less about a larger connection," David Ayer prefaces. "But Joker killed Robin and Batman basically smashes his teeth out and locks him up in Arkham Asylum. It’s in the asylum where Joker would have done the ‘damaged’ tattoo as a message to Batman saying, 'You’ve damaged me. I was so beautiful before and now you’ve destroyed my face.' That’s where the grill comes from."
Most fans will probably wish that scene were featured in Batman v Superman or Suicide Squad rather than simply revealed by the director afterwards but the moments were heavily implied by the two most recent DC Films.
With a standalone Batman film on the way from Ben Affleck (as star, executive producer, and writer), it's possible we will see an adventure of Batman and Robin, be it through flashbacks or an overall prequel setting.
Suicide Squad is now in theaters; Wonder Woman is coming on June 2, 2017; followed by Justice League on November 17, 2017; The Flash on March 16, 2018; Aquaman on July 27, 2018; Shazam on April 5, 2019; Justice League 2 on June 14, 2019; Cyborg on April 3, 2020; and Green Lantern Corps on July 24, 2020.