Ilkay Gundogan revealed Jurgen Klopp was one of the first to congratulate him after Manchester City beat Liverpool to the Premier League title on Sunday.
Gundogan came off the bench to score twice as City came from a 2-0 deficit to defeat Aston Villa 3-2 at the Etihad Stadium on Sunday.
The win meant Klopp's Liverpool remained a point from City in the race for the Premier League, but that did not stop the 54-year-old from getting in touch.
Gundogan played under Klopp at Borussia Dortmund between 2011 and 2015, before the latter left for Anfield, and the 31-year-old revealed his former boss was quick to put his own ambitions aside.
"He was one of the first," Gundogan told Sport1. "We have always treated each other with the utmost respect. He had another very good season with Liverpool and made life extremely difficult for us. He's just an outstanding guy and coach, and he's shown that over the years.
"That was absolutely unbelievable. The fact that we won the title in front of a home crowd in this way was really picture-perfect. The stadium literally exploded, we just cried out our joy and relief.
"We had to play our absolute maximum for 38 games and couldn't afford to be careless because Liverpool were lurking at every second. It was a great end to a long and nerve-wracking season."
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In Sergio Aguero's absence, City's midfield has had to carry added responsibility in goal output and Gundogan has been a steady contributor in that regard, backing up last season's 13 goals with eight in the Premier League this term.
Reflecting on the win over Villa and the wider context of the game, he believes that his winning goal ranks as the most important of his career.
"Based on the ending, I would say yes - and definitely one of my most emotional ones," Gundogan said. "The goal in the 2013 Champions League final for BVB against Bayern [Munich] was also important, even if it wasn't enough in the end.
"On Sunday, a great deal of pressure was lifted because we struggled so much over the entire 90 minutes and we knew that Liverpool was breathing down our necks."