The 16-year-old will begin his professional career with Juventus after confirming his departure from the Blues
The 16-year-old had already been training with the Serie A giants since July but his contract is yet to be confirmed.
Chelsea initially hoped to convince Iling-Junior to remain at Stamford Bridge by offering him his first professional contract, but feared losing him after the Bianconeri joined the race to land him in May.
The England Under-17 international confirmed he has left the Blues in a post on social media on Sunday and expressed his gratitude to the club for their role in his development.
“Full of vast emotions, being at Chelsea from such a young age has truly built me, not only as a the player I am today but also as a person,” he wrote in an Instagram post.
“It’s been a blessed journey and I’m deeply thankful for all those in the Academy. From the groundsmen, kitchen staff, players, coaches, the list goes on.
“I’m filled with gratitude at the time and effort put into my development, leading me to where I am today.
“I would also like to give thanks to the people around me, my family and friends who have consistently supported me.
“Finally, I’d like to thank God for blessing me with this opportunity and protecting me throughout. This is just the start.
“I wish Chelsea all the best for the seasons ahead.”
While the Blues have said goodbye to one highly-rated prospect, they are expected to welcome more players to west London this summer.
Thiago Silva, Malang Sarr and Ben Chilwell are the latest to join Frank Lampard’s side in the current transfer window, following the signings of Timo Werner from RB Leipzig and Hakim Ziyech from Ajax.
Meanwhile, the Premier League outfit are expected to complete the signing of Kai Havertz before the new season begins.
The 21-year-old attacking midfielder is reportedly on the verge of sealing a switch to the English top flight from Bayer Leverkusen in a deal worth £90 million ($120m).