LONDON (AP) — The rainbow flag is flying proudly Thursday above the Bank of England in the heart of London's financial district to commemorate World War II codebreaker Alan Turing, the new face of Britain's 50-pound note.

The design of the bank note, which is the most valuable denomination in circulation, was unveiled Thursday before it is formally issued to the public on June 23, Turing's birthday.

The new note, which is laden with high-level security features, completes the bank's rejig of its stable of paper currencies over the past few years. Turing's image joins that of Winston Churchill on the five-pound note, novelist Jane Austen on the 10-pound note and artist J. M. W. Turner on the 20-pound note.

All the notes are made from polymer rather than paper, which means they should last longer and remain in better condition through their use.

Like the 20-pound note, which entered into circulation a little more than a year ago, the new 50-pound note incorporates two windows and a two-color foil that designers say will make it very difficult to counterfeit. There is also a hologram image which changes between the words “Fifty” and “Pounds” when the note is tilted from side to side.

Turing was selected as the new face of the 50-pound note in 2019, recognition for his pivotal role in breaking the Enigma code in World War II that historians say may have helped shorten the conflict by at least two years, saving millions of lives.

“There’s something of the character of a nation in its money, and we are right to consider and celebrate the people on our bank notes," Bank of England Gov. Andrew Bailey said.

“Turing is best known for his codebreaking work at Bletchley Park, which helped end the Second World War. However, in addition he was a leading mathematician, developmental biologist, and a pioneer in the field of computer science. He was also gay, and was treated appallingly as a result."

During World War II Turing worked at the secret Bletchley Park code-breaking center, where he helped crack Nazi Germany’s secret codes by creating the “Turing bombe,” a forerunner of modern computers. He also developed the “Turing Test” to measure artificial intelligence.

After the war he was prosecuted for homosexuality, which was then illegal, and forcibly treated with female hormones. He died at age 41 in 1954 after eating an apple laced with cyanide.

Turing received a posthumous apology from the British government in 2009, and a royal pardon in 2013.