Elliot Giles ran the second-fastest indoor 800m of all time in Poland on Wednesday to break Sebastian Coe's long-standing British record.
Giles' time of one minute, 43.63 seconds took well over a second off Coe's national record of 1:44:91, which the double Olympic 1,500m champion set in 1983.
Fellow Brit Jamie Webb also ran inside the previous mark, finishing second in 1:44.54 at the meet in Torun.
"I'm still trying to process what even just happened," Giles, 26, said. "It really does feel like a blur.
"I can't believe I just ran 1:43 indoors. I can't put into words right now how it feels. I'm so overwhelmed by it all. It feels like I'm on cloud nine."
Giles' time is second only to Denmark's Wilson Kipketer, who set the world record of 1:42.67 at the 1997 World Indoor Championships.