The relationship between a football manager and a referee is often a strained one and former official Mark Clattenburg has revealed a tense and bizarre exchange he once had with Jurgen Klopp.
The duo did not always see eye-to-eye in the Premier League when Klopp was at Liverpool, but this incident pre-dates the German's time in England.
In fact, the pair swapped pleasantries for expletives after Clattenburg officiated a Champions League tie during Klopp's spell as Borussia Dortmund boss in April 2014.
As one of England's most experienced referees, Clattenburg was tasked with Dortmund's quarter-final first leg at Real Madrid - which they subsequently lost 3-0.
Goals from Gareth Bale, Isco and Cristiano Ronaldo saw the Spanish giants cruise to an easy win but it was a post-match act by Clattenburg that worsened Klopp's mood.
Speaking on the latest episode of The Overlap Fan Debate, brought to you by Sky Bet, the ex-official revealed how a request from Real left-back Marcelo - who was injured at the time - sparked a war of words between himself and Klopp.
'I had a big run-in with Jurgen but I was lucky because it was at Real Madrid, he was the Dortmund manager and they'd just been beaten 3-0,' he reminisced.
'I thought I had a good game. It was Marcelo, the full-back, crazy, but he says, "Can I have a picture?". I'm like, "What with me?" and he said, "Yeah, can I have a picture?". Referees never get pictures with players.
'I said, "Yeah, of course". And I'm standing outside my dressing room, and his wife was there and some of his family - and Jurgen came past, and he went, "F***ing hell. Is that why we got beat f***ing 3-0?".
'I turned around and I said "You're f***** lucky that you got beat 3-0, f*** off". Everybody laughed but I was pleased I was in Real Madrid and not Dortmund, because I would have had to get out of Dortmund alive.'
That dialogue may have proven as motivation for Klopp in the return leg as Dortmund won 2-0 - a scoreline that wasn't enough though as Real prevailed 3-2 on aggregate.
Eighteen months later and Klopp joined Liverpool - sparking more regular run-ins with Clattenburg.