The finish line of Sunday's Allstate Hot Chocolate 15K Run was life-changing for Chicago Police Sgt. Mike Nowacki, his girlfriend, and a complete stranger with "serendipitous" timing.

The 19-year-veteran of the Chicago Police Department and SWAT medic planned on proposing to his girlfriend of several years, Chicago Police Officer Erin Gubala, who was stationed at the finish line of the 9-mile race, but when he approached the end, rehearsing his lines in his head, he put his plans on hold to answer the call of duty.

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"I hear people screaming, 'medic, medic,'" Nowacki said during a press conference Monday. "As a police officer, we go toward the sound of gunfire and then as a SWAT medic we also have that instinct to go toward the sound of someone calling 'medic.'"

Gubala heard her boyfriend's call sign saying he was administering CPR, which put her on pins and needles waiting to see what would happen in the life-or-death situation.

"Before I knew it he was running at me, crossing the finish line," she said. "He got down on one knee and I thought that he was hurt, and then he said, 'Erin, I don't know what to say,' and then I realized what was going on..."

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Nowacki said, "Will you marry me?" but it was a blur for the couple.

Gubala added: "I finally did say yes."

"It was definitely a serendipitous moment," Nowacki said. "Because if I had run a little bit slower or a little bit faster I never would've encountered the young lady," and turning to his fiance, he added, "and then she had to say yes after that."

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The two are planning a "simple" wedding, but Nowacki said he won't be wearing the SWAT gear on the big day.