Norwich manager Paul Lambert will always view Martin O'Neill as "the gaffer", but is all set to tackle his old boss head on at Sunderland.
Lambert worked under the Northern Irishman at Celtic as the Bhoys enjoyed a hugely successful spell, reaching the 2003 UEFA Cup final, winning three Scottish Cups, the Scottish League Cup and the Scottish Premier League title three times, as well as playing in the Champions League group stages.
Lambert has often been compared to his former manager, who like the Scotsman had spells in charge of Wycombe and, albeit briefly, Norwich.
And the 42-year-old feels if he can emulate O'Neill's achievements, it will be a job well done.
"My five years at Celtic under him was a major part of my career and you learn a lot," Lambert said. "He is brilliant at getting the best out of people, playing with confidence. I loved playing under him. It was terrific."
"Whenever I needed advice, I knew I could pick up the phone to him. I would never call him by his first name in case I get fined still.
"I have too much respect for him and what he has done."