what was the first year that the first black hole was sited?

Question: what was the first year that the first black hole was sited?
- Keywords:
  black hole,
  discover
Asked by anon-219136 to Bella on 21 Jun 2019.
- Bella Boulderstone answered on 21 Jun 2019:
  
  The first black hole that is thought to have been seen is the one in Cygnus X-1 which was seen on a rocket flight in the 60s and it was a super strong source of x-rays.
  
  The first image of a black hole ever taken was this year: https://www.youtube.com/watch?v=S_GVbuddri8

Question: what was the first year that the first black hole was sited?