Ciara Mageean was the first to congratulate Faith Kipyegon after the Kenyan broke the 1500m world record.
Kipyegon is a two-time Olympic champion but had previously come agonisingly close to breaking the world record of 3:50.07 held by Genzebe Dibaba.
But at the Florence Diamond League meeting on Friday, the 29-year-old sprinted all the way to the line to win in a time of 3 minutes 49.11 seconds and become the first woman to break the 3:50 barrier.