(CNN) Secretary of State Mike Pompeo attended an off-the-books sit-down meeting with a conservative group that included a small number of wealthy Republican donors, which was not on his official schedule while he was in London to attend this week's NATO Summit.

The gathering, hosted by the Hamilton Society, conveniently took place in the hotel where Pompeo was staying, situated in a small events space on the second floor. Pompeo slipped into the meeting, without the State Department alerting the press traveling with him about where he was headed or who he was going to meet.

CNN reviewed a copy of the meeting invitation and spoke to multiple people who attended. The Hamilton Society is a group of right-leaning American and British business professionals who often invite guest speakers to meet them.

The news that he made time to meet with the donors after a busy day visiting with world leaders only serves to heighten speculation that Pompeo may be eyeing a run for the Senate in Kansas next year and as he has become further embroiled in the Ukraine impeachment inquiry.

The few dozen attendees had to leave their cellphones outside of the room for the evening, to ensure that nothing Pompeo said would be recorded, two attendees said. Though they made clear that Pompeo had no reason to believe he was walking into a contentious conversation.

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