Romelu Lukaku has become the latest player to make a high-profile return to his former club after going back to Chelsea.
The striker signed for the Blues in 2011 but only made 15 appearances for the club before moving to Everton in 2014.
Here, the PA news agency takes a look at some other top players who returned to former clubs having been allowed to leave earlier in their careers.
Paul Pogba
In 2016 Manchester United spent £89million to bring Pogba back from Juventus. Pogba had spent time with United's academy as a teenager but became frustrated by his lack of game-time and left in 2012. He established himself as one of the best players in the world during his time in Turin, and for the France national team, before returning to Old Trafford four years later.
Mats Hummels
Having started out with Bayern Munich's academy, Hummels made his name with Borussia Dortmund, initially on loan and then as a permanent signing from 2009 to 2016. The centre-back won two Bundesliga titles and two German Super Cups and established himself in the Germany set-up. Hummels returned to Bayern five years ago for a reported fee of around £34million before heading back to Dortmund in 2019, again for a fee over the £30m mark.
Nemanja Matic
Chelsea spent £1.5m to bring Matic to Stamford Bridge in 2009. The defensive midfielder made two substitute appearances in the Premier League then had a loan spell at Vitesse Arnhem before moving to Benfica in 2011. In 2014 Jose Mourinho quickly identified Matic as a key target after impressing in Portugal and spent £21m to bring him back to Chelsea. Matic went on to reunite with Mourinho at Manchester United in 2017.
Gerard Pique
Before he became an integral cog in one of the most successful teams of all time at Barcelona, Pique spent four years at Manchester United. The centre-half moved to Old Trafford from Barca's youth academy in 2004 and featured 12 times for United in the Premier League. He struggled to hold down a regular first-team spot and rejoined Barcelona in 2008 for £5m.
Marco Reus
Reus started his career at Borussia Dortmund before joining Rot Weiss Ahlen at the age of 17 in 2006. He made his name at Borussia Monchengladbach and became a key part of their set-up. Dortmund soon took note and splashed out over 17m euros to bring him back in 2012.
