Lily Stewart, the University of Georgia student who went viral last week for her mug shot, allegedly gave cops an interesting explanation for trying to avoid her second arrest … officers say she told them she tried to flee because she was out on bond.

Lily, as we first reported, got busted again over the weekend — on charges of obstruction of a law enforcement officer and loitering/prowling — and now we know why.

According to the police report, obtained by TMZ, cops responded to an intrusion alarm at the UGA student center around 3 AM Sunday and observed Stewart and 3 others inside the building.

Police say Lily eluded officers for a few minutes … until she was found crouching behind a brick wall outside the school’s football stadium, which is next to the student center.

Cops detained Lily, and when they started questioning her, they say she told them, “I didn’t want to get caught doing anything bad because I am out on bond right now.”

Cops say she added, “Was it the trespassing? Truly that was actually my fault.”

Officers say another UGA student who was part of the group claimed they were just trying to get back to their sorority.

The officer did note that he observed no signs of alcohol consumption while speaking to Lily.

All four were arrested and taken to Athens-Clarke County Jail. Lily’s been there before … the whole reason she’s famous is because she was snapped in a viral mug shot during her previous arrest on a speeding charge earlier this month.