TORONTO, Aug 12 (Reuters) - Royal Bank of Canada's ( RY )

former CFO Nadine Ahn has filed a wrongful-termination

lawsuit against the bank, and alleged that "gender-based

stereotyping" was at play in her dismissal.

In April, RBC, Canada's biggest bank, said it had terminated

Ahn after its investigation found she was in an undisclosed

close personal relationship with another executive that led to

preferential treatment of the executive, including promotion and

compensation increases.

Ahn, 53, said in a lawsuit filed in the Ontario Superior

Court of Justice on Aug. 8 that the bank's allegations are

"patently false" and her successes, career, and reputation were

destroyed in an instant by the bank.

She has sued RBC for nearly C$50 million ($36.38 million).

"(RBC) failed to provide her with a fair opportunity to

respond to the allegations, and the bank was, at least in part,

motivated by stereotypical assumptions concerning friendships

between women and men," Ahn's lawyer wrote in the lawsuit.

Ahn alleged in the lawsuit that she was "ambushed" by RBC's

external counsel on April 5 and questioned for two hours. She

added that the bank seized her laptop and her work and personal

cellphones.

The lawsuit stated that RBC did not provide Ahn with a copy

of a co-worker's complaint or the particulars of the allegations

against her. It said RBC did not allow Ahn to postpone the

meeting to obtain legal advice.

Ahn also alleged RBC had already decided to replace her at

the time she was questioned, as it announced her dismissal and

the appointment of Katherine Gibson as interim CFO the same

evening.

In a statement, RBC said Ahn's claims are without merit, and

that it would vigorously defend against them in court.

RBC said Ahn and the co-worker, Ken Mason, had engaged in an

undisclosed close personal relationship leading to preferential

treatment for Mason, including promotion to vice president.

"The facts are very clear that there was a significant

breach of our code of conduct based on the irrefutable evidence

collected during the investigation," RBC said in its statement.

Mason is suing the bank for about C$20 million for wrongful

termination and denies he and Ahn had a close personal

relationship.

"RBC as a whole has been an environment for 'old-boys-club'

cronyism," his lawsuit, also filed Aug. 8, said.

RBC said that the claims in Mason's suit are also without

merit and that it would defend against them.