Vivat Regina - Long Live The Queen

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LONDON, England (CNN) -- Queen Elizabeth II was set to become Britain's oldest reigning monarch on Thursday, surpassing the record set by her great-great grandmother Queen Victoria.

Queen Elizabeth II ascended to the throne in 1952.

By early Friday, the queen will be 81 years and 244 days old. Victoria died in 1901, having lived 81 years and 243 days.

A spokeswoman said Buckingham Palace had heard from historians and observers that the milestone would come around 5 p.m. (noon ET) Thursday.

The record is different from that of the longest-serving monarch, which belongs to Queen Victoria, who reigned for nearly 64 years. Queen Elizabeth ascended to the throne in 1952, meaning she has served 55 years.

The queen was born at 2:40 a.m. on April 21, 1926. 11 prime ministers, starting with Winston Churchill, have served during her reign.

Buckingham Palace said the queen would not be marking the day with any special events or public engagements, but would be "working as normal."