Edimilson Fernandes left West Ham for Mainz for around €9 million (£7.4 million) in the summer of 2019, as reported by Viola Nation.
The 23-year-old joined the Hammers from FC Sion for around £5 million in the summer of 2016 (BBC Sport).
Fernandes, a 14-capped Switzerland international, never really established himself at the London Stadium, however.
The midfielder made 48 appearances for West Ham, racking up one goal and one assist in the process, but in fairness to him, only 22 of those outings were starts.
The Swiss star is a box-to-box type midfielder with bundles of energy and athleticism. Sounds like the kind of player the Hammers desperately need at the moment.
The east London outfit chose to move him on eight months, ago, however.
So how has Fernandes got on in Germany since leaving the Hammers?
The Switzerland international has made 15 Bundesliga appearances for Mainz this season, and has failed to register either a goal or an assist (Transfermarkt).
In those outings, he has averaged 34.9 passes per game with an impressive completion rate of 86.4% (Who Scored).
Fernandes has also averaged 1.7 tackles, 1.8 interceptions, 2.8 clearances and 0.5 blocks per game during those outings (Who Scored).
So it is clear to see that the 23-year-old puts in a defensive shift on a consistent basis.
His team are struggling, however. They are currently sitting in 15th spot in the Bundesliga table, just four points clear of the drop zone.
And Fernandes will obviously be hoping to help his team climb away from the bottom three between now and the end of the season.
Should West Ham have kept the midfielder last summer? In truth, the jury is still out.