"I got the 411. She got engaged Saturday night. There is a ring," Frankel, who's had her share of drama with Lesseps on the Bravo reality series, toldAndy Cohen's Sirius XM show Radio Andy on Monday.
"I think it's a yellow diamond and it's decently large, and she called Page Six right after so, it's a normal engagement! You know what I mean? Isn't that what everybody does?"
While one might sense a little sarcasm in her voice, Frankel clarified, "I'm actually, I'm happy though. Like, if she's happy... I had a good feeling, I don't know about him or them or whatever."
Frankel then revealed D'Agostino previously dated Housewife Ramona Singer and used to be "friends with benefits" with Housewife Sonja Morgan, so the ladies gave her "a little intel recently."
Cohen laughed at the remark and said, "What are the chances," to which Frankel replied, "On Housewives, very high. He's the new Harry Dubin. Harry Dubin for those anybody who hasn't watched the Housewives is the other man who banged every Housewife except for like [Porsha Williams], I think."
Frankel, who previously starred on Bethenny Ever After and had her own talk show, then spoke some kind words about Lesseps.
"What's funny is, you know, how I can't hide my feelings about things or [my] opinions, and I feel happy," she told Cohen. "I feel excited for [LuAnn]. She's having a moment. It's exciting. She wasn't that happy this summer, and I feel like who knows, I suck at relationships. I'm not one to talk about anyone's relationship. I'm in the 12 year divorce."
Frankel filed for divorce from her estranged husband, Jason Hoppy, in January 2013. Their split was anything but amicable, as they've been dueling in court over their finances ever since.
As for Lesseps' engagement, D'Agostino reportedly popped the question in honor of Valentine's Day.
"Thomas just couldn't wait and gave Luann an 8-carat canary yellow diamond ring. Luann is 'over the moon' in love with Thomas, considers him her soul mate and is so happy and grateful to have found love a second time," Lesseps' representative toldUs Weekly in a statement.
"The two were introduced by their mutual friend and another RHONY cast member, Dorinda Medley, a few months ago and have been inseparable ever since. The happy couple are celebrating jetting off for a ski vacation in Vail, Colorado, this week."
Lesseps was previously married to Count Alexandre de Lesseps from 1993 to 2009 and the pair share two adult children.