Twenty-two years.
Twenty-two years had to pass in order to have a Grand Slam Champion not named Roger Federer, Rafael Nadal or Novak Djokovic. Keep in mind the count is still going for a Grand Slam not to feature a finalist not named Federer, Nadal or Djokovic (who made it to the Australian and Wimbledon, but fell short on both occasions).
Congratulations to Jannik Sinner. I watched him play five years ago and I knew he was going to win the US Open one day.
Hr