Pierre-Emerick Aubameyang was a great servant to Borussia Dortmund.

The Gabonese international joined the club in 2013 and would go on to enjoy four-and-a-half successful seasons.

In all, he made 213 appearances and hit the back of the net 144 times.

He finally left in 2018 as he joined Arsenal for £60 million.

While Aubameyang has enjoyed great personal success since his move, Arsenal have struggled.

The Gunners have failed to qualify for the Champions League in each of the past three seasons. They came close last season but ended up missing out after losing the Europa League final.

Dortmund, on the other hand, have been on the rise since Aubameyang's departure.

Despite losing a player of great quality, they have re-emerged into one of Europe's best clubs and narrowly missed out on the Bundesliga last season.

Dortmund are back in the Champions League this season and play Slavia Prague in their second group game on Wednesday.

And ahead of the game, Dortmund's CEO decided to take a swipe at Aubameyang.

Not only did Hans-Joachim Watzke hint that the 30-year-old left for money, he also mocked him for not playing in the Champions League.

"Aubameyang, who plays great at Arsenal, will probably be warm-hearted when he looks at his bank account, but on Wednesdays, will be saddened when he has to watch the Champions League on television," Watzke told Suddeutsche Zeitung, per the Metro.

"Some [players] go to clubs because of this money, where they have not played Champions League for years."

Ouch. Aubameyang was a goal-machine at Dortmund but there's clearly a few left at the club that are still bitter about his departure.

Meanwhile, Aubameyang has been in great form for Arsenal and has scored 17 goals in his past 17 games.

And the Gunners are keen to reward him. According to the Daily Mail, Aubameyang currently earns £200,000-per-week but the club have opened talks with him over a contract extension thay would see him given a significant pay rise.