The left-back’s wonderful strike put Peterborough United on their way to defeating Birmingham City in the Vertu Trophy final.
Posh fans will be singing his praises after they overcame the Tom Brady-owned favourites at the National stadium, and the National League South side played an important part.
Mills spent a valuable two months on loan at the Queen Elizabeth II Stadium at the start of the season, before being recalled by his parent club in November.
The 19-year-old picked up vital experience in his eight weeks with the Towners, playing a total of eight games and 710 minutes before returning to London Road - and thrusting himself into the first team.
“I can't put it into words,” he said after the game to CBS Sports. “I was on loan at Enfield and that did me the world of good at the start of the season.
“So to come here and score, keep a clean sheet and beat Birmingham in the final, it's an unbelievable feeling”.
Enfield Town took to twitter to congratulate their former player on his goal and his performance, posting: “From Donkey Lane to scoring at Wembley, Congratulations Harley”.
It was also a good weekend for the North London club, after their fans watched them take a giant stride towards safety after their victory against Chelmsford City.
The Towners currently sit six points above the relegation zone with three games to go, meaning it is seven games unbeaten with four wins.
Mills took this valuable experience and used it this weekend with his Man Of The Match performance under the Arch.
The Posh saw off League One champions Birmingham 2-0 after Mills opened the scoring, his incredible 30-yard free-kick has been labelled as one of the best goals scored at Wembley since the rebuild in 2007.
“I practice them all the time in training but I don't think one's ever gone in that well,” he said. “In the moment you don't feel like you're in a final at Wembley, it's just repetition.
“Ever since I was a really young boy my dreams have been to play at Wembley and score”.
Peterborough then doubled their lead just before the half as Hector Kyprianou’s lovely finish settled the nerves.The Posh then saw out the second half ending victors and also becoming the first ever team to win the Vertu Trophy on consecutive occasions.