The 'Mirrors' hitmaker was a partying with his entourage of 25 until 4.20am at the Crystal Cologne club in the German city, after being invited by the nightclub owner to enjoy drinks on the house following a concert at the Lanxess Arena.

The staff were left "amazed" with the generosity of the 33-year-old singer - who is married to 'Playing for Keeps' star Jessica Biel - and his "mood" throughout the night.

Club manager Yunus Arslan, 40, told The Sun newspaper: "He was in a great mood, a real gentleman."

Nina Blum, 28, who was among staff serving him, added: "We were all really amazed."

Although his tip was very generous, the 'Suit and Tie' star could more than afford it as earlier this month, Billboard's annual Money Makers list showed he earned a reported $34.1million in the US in the last year.

Justin's 'The 20/20 Experience World Tour' kicked off in November last year when he performed at the Barclays Center in New York and has since had a number of sparkling reviews.

He is next set to take to the stage Berlin on April 24 while he is on the European leg of his tour before he heads to Asia.