Following Prince Harry and Meghan Markle stepping down as senior members of the royal family, Queen Elizabeth is making efforts to move the monarchy forward. Her Majesty recently took on a secret mission to one of the U.K.'s top security agencies, MI5.

She praised intelligence officers for their response to changing threats to the UK in her secret visit. These threats are events the U.K. has been facing since World War 2.

On Tuesday lunchtime, the Queen was photographed discussing with MI5 Director General Sir Andrew Parker outside the headquarters in London.

The 93-year-old monarch's visit came with the goal of expressing gratitude for their tireless efforts to keeping the country safe. Parker who gave her a personal tour of the domestic spy facility.

Her visit was purposely kept discreet in order to avoid the media and maintain the decorum of the security agency.

Dressed in an elegant plum coat and matching wide-brimmed hat, she thanked them for the tireless efforts to keep our country safe.

She said, "I would like to take my visit here today as an opportunity to thank you all. I am always struck by the remarkable resolve with which you carry out your vital role."

The Queen issued a speech for U.K.'s domestic counter-intelligence and security agency at Thames House.

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"There will no doubt continue to be significant threats and challenges ahead. But on each of my visits to MI5, I have been impressed by the way that you have adapted to the changing threats to our nation," she stated.

Queen Elizabeth II added, "Whether responding to the threats from the Nazis or the Cold War, domestic terrorism or the cybersphere, you have always demonstrated the utmost commitment to your motto: 'Regnum Defende'.

Regnum Defende means 'Defend the Realm.'

She also silently acknowledged her father's key role in the run-up to the D-Day landing. The monarch did not mention if she was involved in World War 2.

Parker discussed how King George VI carried out diversionary royal visits to misinform the Nazis.

The Queen viewed exhibits in the institution's museum and had a private briefing. The exhibits in the MI5 museum included displays underscoring the work of WWII double agents GARBO and TATE, who were integral to the major deception operations against Germany.

Parker described the MI5 double agent operation as "the most important thing MI5 has done."

Her father, King George VI, tricked the enemy by visiting a fake oil storage depot in Dover built by Shepperton film studios on behalf of the War Office.

Given the propriety of the security agency, few details about the event have been shared publicly, including the Queen's speech addressing the staff.

The surprise visit came when Buckingham Palace confirmed the Duke and Duchess of Sussex will be leaving the royal family on March 31.

Read the Queen's full speech here or watch below:

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