Union Berlin managing director Oliver Ruhnert cut a frustrated figure after seeing their top scorer, Taiwo Awoniyi officially leave the club on Saturday.
The 24-year-old was confirmed a Nottingham Forest player on Saturday, penning a five-year contract.
Awoniyi was the first arrival at the City Ground since the club’s promotion to the Premier League.
Steve Cooper’s side paid a club record £17.5m fee to secure his services.
Union Berlin made significant profit on a player they bought for £7m from Liverpool last summer.
“It was clear that a player like Taiwo will attract the attention of other clubs with his performances,”Ruhnert told the club’s official website.
“From a sporting and personal point of view, he is a great loss for our team, which must now be absorbed.
“We wish Taiwo all the best for the future and thank him for his achievements in the shirt of 1. FC Union Berlin.”
Awoniyi scored 20 goals in 43 games across all competitions for Union Berlin last season.
He spent two seasons at the club, the first on loan.