When Canada was designing its current $20 bill, it considered dispensing with its "tradition" of depicting the reigning monarch if Queen Elizabeth dies or abdicates, internal documents from the country's central bank showed.

The issue of Elizabeth's potential death came up several times at the Bank of Canada between 2007 and 2015, according to documents obtained by Reuters in October under access-to-information laws.

The longest-reigning British monarch, who is also the sovereign of Canada, Elizabeth appears on all standard Canadian coins, but only one banknote, the $20 bill.

The 90-year-old Elizabeth, head of state of 16 Commonwealth countries including Canada, has reigned since 1952 and remains popular in Canada. A recent visit by her grandson Prince William and his family drew enthusiastic crowds.

Still, not all the royals appear so popular. A poll by Forum Research last year found more than half of Canadian

adults do not want Elizabeth's oldest son and heir Prince Charles, who will ascend to the throne immediately upon his

mother's death, as head of state.

'Matter of tradition'

In the documents, central bank staff working on the 2012 $20 bill wrote that depicting the reigning monarch was

"a matter of tradition."

"In the event the Queen dies or abdicates before the new notes are issued, a decision will need to be taken as to whether to continue this tradition or to replace the image" with some other portrait subject, a 2008 policy advice paper read.

Staff were concerned about the increased costs and delays of reworking designs if the monarch changed before the design process was done, the documents showed.

While plans were made for subjects to replace Elizabeth, those were unclear as parts of the files were redacted.

Staff wrote in one document that candidates would need to be dead, and potential ones would be chosen based in part on a "public opinion poll."

Bank of Canada spokeswoman Josianne Menard said in an email the files represented only "contingency options" and staff's "due diligence," and what ultimately goes on a note is up to the country's finance department.

The department did not directly respond to questions on the matter, saying it was focused on previously announced plans to feature a Canadian woman on an upcoming banknote in the 2018 series.

"No other changes are being considered at this time," it said without elaborating.

Buckingham Palace, the official residence of Elizabeth that also handles queries for Charles, declined to comment.