US sprinter Allyson Felix breaks one of Usain Bolt's world records

USA Olympic sprinter Felix broke Bolt's record Sunday after winning her 12th gold medal at the World Championships on the mixed-gender 4x400m relay team. 

She now holds the record for the most gold medals at the track and field World Championships.

Felix is already one of the most decorated track and field athletes, winning a combined nine medals between each of her four Olympic games. Six of the medals are gold.

Felix summed up her response to the honor in one word on Twitter: "Humbled."

Another big accomplishment for Felix, it's her first season as a mother. But her journey back to the track has not been an easy one.

In November 2018, Felix battled preeclampsia and underwent an emergency C-section at 32 weeks to deliver her daughter.