High-flying executive Nadine Ahn appeared to be riding a wave of success earlier this year after a $C13.5 billion ($14.7 billion) mega-deal cemented her status as one of the most powerful women in banking.

By overseeing Royal Bank of Canada’s (RBC) acquisition of HSBC’s Canadian arm, the married mother of three steered the country’s largest-ever banking takeover. The deal appeared to be the crowning glory of Ahn’s 25-year career at RBC, having risen through the ranks to become the bank’s chief financial officer. Nadine Ahn was sacked by RBC for allegedly having an illicit 11-year relationship with a colleague, Ken Mason, and helping him secure large pay rises and promotions.

But today it looks increasingly likely to be her epitaph. Just weeks after the deal was completed, Ahn was sacked by RBC for allegedly having an illicit 11-year relationship with a colleague, Ken Mason. In court documents seen by The Telegraph , RBC implied that the pair’s relationship went beyond just professional matters, alleging that she helped him secure large pay rises and promotions.

Ahn has denied the claims, sparking a bitter legal battle in Canada over whether RBC acted improperly by sacking both her and Mason. She is seeking $C50 million ($54.4 million) in damages from RBC, claiming that her unfair dismissal led to her suffering “devastating, worldwide reputational harm”.

Loading Mason is also suing the bank. The dispute throws an unwelcome spotlight on RBC, a lender worth $C216.