Prince Harry begins work on mystery project at London studio

Prince Harry may be back in the UK as a 'private citizen' and not a 'working royal', but that didn't stop him from going back to work.

Prince Harry spotted at studios

The Duke of Sussex was spotted spending a full day at a London studio working on a mystery project.

On Monday, Tower Bridge Studios, a video and podcasting studio in London, shared photographs of Harry signing their celebrity wall.

Sharing the photos on Instagram, they wrote, "Thank you Prince Harry for choosing Tower Bridge Studios! It was an absolute pleasure to have you in our studios and signing our wall... we look forward to welcoming you back again."

Harry begins work on mystery project

As per a report on People, Harry visited the studio on Friday, September 4, and spent most of the day working on an undisclosed “mystery project”.

Before leaving, he made sure to keep up with the studio’s tradition and sign his name to the celebrity wall.A source at the studio described Harry’s visit as relaxed and said he was friendly with staff. “He was very, very pleasant to everyone,” the source told PEOPLE. “And he was very pleased to sign our celebrity wall. It was all very relaxed.”

King Charles clarifies son Harry's status

The post also comes just as King Charles III authorised the release of a letter on Monday clarifying the status of Prince Harry and his wife, Meghan, now that they've returned to the UK.

The letter confirms that the couple are no longer working members of the royal family and will not use the titles “his or her royal highness.'' It adds that any security issues are the responsibility of relevant police agencies and the couple's charity work will be carried out in a private capacity.The letter states that the king authorised the communication "to help avoid doubt or confusion" about the couple's status.