A former client advisor for Spanish customers at Swiss bank UBS is facing criminal charges after allegedly cheating wealthy clients out of around 20 million Swiss francs ($23.99 million), a Swiss newspaper said on Sunday.

Switzerland's SonntagsZeitung quoted Markus Fasano, a prosecutor of the Zurich-Sihl Public Attorney's Office, as saying it had started investigations into the client advisor at the start of April 2010.

The process against the involved party is still in the stages of police investigation, Fasano was quoted as saying.

According to the newspaper, the client advisor was working with ultra high net worth clients in Spain.

A spokesman for the bank declined to comment on the figure but said: UBS confirms that inconsistencies in its business with Spanish clients were discovered in early 2010.

UBS filed criminal charges, and the involved client advisor was laid off without notice. All affected clients were reimbursed by UBS.

($1=.8335 Swiss francs)

(Reporting by Katie Reid; Editing by Greg Mahlich)