“Sooo much to be THANKFUL for!!!,” she captioned an Instagram photo of herself and Kluth kissing on Thursday for Thanksgiving, with her left hand touching Kluth's cheek so fans can see the big ring.
He's an entrepreneur who set up the business CouponCabin.com, which provides online coupon codes.
Mortimer's ring is a large oval-shaped solitaire that swamps her finger, and looks different from her previous three-stone ring from ex-husband Topper Mortimer.
RHONY followers first saw Kluth, 40, when Mortimer, 44, and Carole Radziwill went on a double date -- which was a blind one for the blonde reality star.
The two hit it off, but after that, frequently split up and then reconciled.
A video of the proposal showed Mortimer wearing a long puffy black jacket and standing as Kluth got down on one knee holding up a box with the ring inside.
She covered her face but quickly bent down to hug and kiss Kluth. E! News first reported the engagement.
Christmas carolers were singing on the steps behind the couple in a video posted by an onlooker of the engagement.
Mortimer gushed over her recent mid-western vacation, posting a photo on Instagram in which she kissed her beau in Chicago.
“Best weekend ever!!!!” she wrote as a caption for the video she posted.
A source told RadarOnline.com after Mortimer and Kluth rekindled, “They realized they still love each other, and they are giving it another go.”
But she said at a recent RHONY panel, “Scott and I did get back together. I’m more excited than anybody is, but I’m just so happy.”
"Relationships are hard when you have the long-distance, even though it’s only about two and a half hours away,” Mortimer noted.
But a big ring clearly takes the sting out of their travel trouble!