Seville showed he belongs in the top echelon when he blazed to world 100 metres gold in 9.77 seconds on Sunday, earning Jamaica’s first 100 title since the last of Usain Bolt’s three in 2015 and becoming the joint-10th fastest man of all time.
“I am extremely elated that finally he has been rewarded with his effort after so often narrowly missing getting a reward in terms of a medal,” Seville's coach Mills told Television Jamaica.
“That has never deterred me because when I started working with him I remember telling him he was not going to be at his best until he matured at around 24 based on what we were working with.
“He has had many, many challenges health-wise which he is still battling with but his ability is undoubtedly world-class. I have done a tremendous amount of work with him and it has taken all my experience and knowledge to really keep him going.”
Seville, who is now at that magic age of 24, is the fourth 100m champion Mills has guided, after Bolt, Yohan Blake and St Kitts and Nevis's Kim Collins back in 2003, plus 2023 world 400m champion Antonio Watson and a host of other leading Jamaicans.
The 76-year-old also said he was not worried when his charge was left in the blocks in the first round in Tokyo and had to dig deep to work his way through to qualification.
“Every now and then, especially after he warms up, he has a problem that occurs, so he decided that he was not going to push off other blocks in fear that his calf may grab him," Mills explained.
"So he came out gentle and then ran to qualify. I wasn't worried because when I minused his reaction time and added his normal reaction time, it comes out to a 9.77 effort.”
At last year’s Olympics Seville was supreme through the heats but finished last in the final – the result, he explained on Monday, of another injury.
This time he backed up his qualifying performances with an electrifying run, leading home a Jamaican 1-2 with Kishane Thompson ahead of American defending champion Noah Lyles in third.
Mills said that they and various medical experts were still trying to get to grips with some of Seville’s bio-mechanical issues but that when they were finally fully dealt with 9.76 would be “just a dip in the bucket.”
“So I'm really happy for him and this will go a long way in continuing to build his development because he's still young and I expect a lot more from him," added Mills. "We're just excited because I think it's just the beginning."