Former President Bill Clinton made an unexpected trip to Colorado on Thursday to rally supporters for wife Hillary's campaign ahead of Colorado's March 1 caucus.

News of this Denver trip was kept limited by the Hillary Clinton campaign to campaign volunteers and top-level supporters, and only became known after people began tweeting photos of the afternoon event.

Secrecy surrounding a trip like this is pretty abnormal for a campaign seeking as much attention as possible, says 7NEWS.

State Senator Andy Kerr, D-Lakewood, and House Majority Leader Crisanta Duran of Denver both tweeted photos from the event. Duran later confirmed the former president's visit to The Denver Post.

A campaign spokeswoman told The Post that "there were no public events on this trip" but did not answer as to why this event was kept secret, nor did the campaign respond to questions about the nature of the visit.