King made his global debut for Great Britain on Sunday in the heats of the 110m hurdles.
Although he went into his preliminary run knowing he was the joint slowest in the race, at the halfway point it looked like he was going to claim a top four finish and progress to the semi-finals.
But it all went wrong for him in the later stages and he ended up eighth in a close heat with a time of 13.67 seconds.
The fourth-placed athlete, Japan’s Genta Masuno, who qualified for the semis only ran 13.58 seconds.
King had run 13.48 second this season and it looked like he was going to challenge that PB time after the start he made at the London Stadium.
Afterwards the 23-year-old City of Plymouth athlete tweeted: “Gutted with the result today. I was in a great position at H6 but smashed a hurdle and went backwards from there. Gave it my all though!”
He added: “Thanks so much to @BritAthletics for the opportunity – thoroughly enjoyed my first World Champs. Hopefully the first of many!”
King’s big British rival David Omoregie also missed out on progressing to the semi-finals, but fellow Brit Andy Pozzi did progress.