Miles left Saints for City, with a seven-figure agreed as compensation.
He later posted: "I'm not sure I’ll ever be able to express what Southampton FC means to me.
"Staplewood Campus has been a home from home for the last nine years and the people there are truly like family.
"From the operations team to the security guards, canteen staff to the education team and the physios who have been incredible at keeping me on the pitch.
"The connections I’ve built are ones I’ll always value as these are the people who have made my experience at this academy very special.
"I’ve been so lucky to have been coached by some top people both past and present, and I hope they know the positive impact they have had on my football development.
"I’m so grateful for all of their guidance, support and opportunity. Lastly the players, well we’ve got some memories haven’t we?
"Whether times were good or bad I’m so grateful to have experienced them with you all. Very privileged to have played with and learnt from some of the very best.
"I will never forget what this club has given me but now is the time to say goodbye. Thank you for everything."