World champion Ronnie O'Sullivan was knocked out of the European Masters by Irish teenager Aaron Hill.
The 18-year-old is ranked 115th in the world after turning professional in March and was not born when O'Sullivan, 44, won his first world title in 2001.
In his first match since winning his sixth world title in August, O'Sullivan fought back from 3-1 down to lead 4-3 but Hill took the last two frames to clinch a 5-4 win in the second round.
"I'm speechless," said Hill.
"If I'd lost after being 3-1 up, I'd have been disappointed. I am just so pleased with that victory."
O'Sullivan looked to have survived a scare when he made a break of 102 to go 4-3 up in Milton Keynes, and then scored first during the deciding frame.
But Hill produced a break of 78 to wipe out a 28-point deficit and book a meeting with world number 33 Matthew Stevens in the last 32.
"I didn't just go out there and be happy to be there - I still wanted to win the match," added Hill.
"Everyone back home, my family and my friends must be buzzing. I just looked at my phone and I think it is going to take until Christmas to reply to everyone."
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O'Sullivan received a bye in the first round after five players had to withdraw because of coronavirus.
Three-time world champion Mark Williams was also knocked out by a tour rookie on Thursday, losing 5-4 to 24-year-old Peter Devlin.
After reaching the World Championship quarter-finals last month, O'Sullivan was asked if he would have believed he and Williams, 45, would still be performing at the top level 26 years after first facing each other.
"Probably not if you asked me then but when you look at the standard of play, I would say yes," he told BBC Two at the time.
"If you look at the younger players coming through, they are not that good really. Most of them would do well as half-decent amateurs, not even amateurs. They are so bad.
"A lot of them you see now, you look at them and think, 'I would have to lose an arm and a leg to fall out of the top 50'. That is why we are still hovering around, because of how poor it is down that end."
Hill responded to O'Sullivan's comments after Thursday's win, saying his words were "in the back of my head".
"I didn't worry about it," he added. "I just said to myself when he said it, that one day I am going to show him what I can do. I think today was the day."