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Tinsley Mortimer could become a “Real Housewife” of Chicago.

The “RHONY” star is engaged to her on-again, off-again boyfriend, Scott Kluth.

Businessman Kluth proposed to Mortimer in his native city on Sunday, Page Six can confirm. The big moment happened as Christmas carolers sang by the steps of the Chicago Water Tower.

“Scott’s apartment is close to where the carolers were,” a source told us. “They were walking to dinner and they saw these carolers, and they broke into Christina Perri’s ‘A Thousand Years,’ which is their song. It took Tinsley a few seconds to figure out what was going on, but then Scott got down on one knee. He’d organized the whole thing with the carolers in advance.”

“She was totally surprised,” the source continued. “Her friends sort of knew something was coming, but it really did take her by surprise. Scott asked her mom’s [Dale Mercer’s] permission, so their families knew, but it was a surprise to her friends.”

Insiders told Page Six on Nov. 1 that Kluth had purchased an engagement ring.

Kluth, 40, began dating Mortimer, 44, after meeting through former “RHONY” star Carole Radziwill, but they frequently broke up and got back together because of the distance between them.

This will be the second marriage for Mortimer, who was previously married to Topper Mortimer from 2002 to 2010.

Meanwhile, Topper and his new wife, Tabitha Simmons, welcomed a daughter last January.