Sunderland have said they were disappointed losing Francis Okoronkwo to Everton.
Everton confirmed his signing following a £1million transfer this week.
Sunderland sporting director Kristjaan Speakman said: “We are disappointed that Francis and his family took the decision to leave the football club earlier this summer, as we demonstrated a clear pathway for him to continue his development into the first-team environment.
“Throughout the summer, we have displayed our ability to retain and attract young talent and we have started to honour our long-term commitment that our homegrown players will be integral to our philosophy and future success.
“Although we are disappointed Francis will not be a part of that process, we wish him and his family well.”