Brandi Glanville is angry at LeAnn Rimes for not informing her that she took her 7-year-old son Mason to the emergency room last weekend.
On Saturday, the country singer, 28, Twittered: "Flew home for 5 hrs to see Eddie [Cibrian] & the lil one's and ended up in the ER! Everybody's fine, just a minor kiddo accident. Boys will be boys!"
Glanville, 36, tells E! News she was shocked she had to learn about the incident via Twitter -- and not from Rimes herself.
"All I know is I didn't get a phone call," she tells E! News. "Poor choice. Bad parenting."
Glanville says she eventually found out her son had split his chin.
"I don't know how exactly it happened, but Mason told me LeAnn had oil on her hardwood floors and he fell," she says. "Eddie didn't bother to call me and I showed up to Mason's soccer game that day only to get a text from Eddie afterwards saying Mason wouldn't be playing since he was in the ER all morning."
A Rimes rep says it was "a minor slip" and that "Eddie and LeAnn were with him the whole time, and he is all smiles now."
Nevertheless, Glanville says she is "disappointed" over the way it was handled.
"I'm the mother of these two boys and if we're going to co-parent, we have to do that together," she says. "It's not call me after."
She also sats it wasn't the first time her children have been hurt under Rimes' eye: Her 3-year-old son Jake sustained an injury while playing on the singer's tour bus.
"The last time they had the boys, Jake ended up getting seven stitches," she says. "I had to call in a plastic surgeon to stitch up Jake's forehead."
Glanville stresses that she doesn't think her boys are in danger now that they're living with Rimes.
"The only thing that's in danger is our co-parenting relationship if [LeAnn] keeps involving herself and doesn't allow [Eddie] to call me," she says.
Rimes recently shot back on Twitter, writing: "To be really honest, it's not her place to tell me how to be. I respect her as their mom, but she has to understand they're in my life. I can talk about my life just like she can [talk] about her's.
"Just so you know, she has never spoken to me," she continued. "This IS my life too and they are in it 50% of the time ... I've stepped into a very tough, but rewarding role ... I treat those boys like they are my own because that's how I love."
Us Weekly first reported that Rimes and Cibrian, 37, famously had an affair shooting a Lifetime movie last year. She later divorced husband of nearly eight years, Dean Sheremet; Cibrian also split from Glanville.
Rimes tells the October issue of Shape that she cheated because she was in an unfulfilling marriage.
The singer explained, "I think any relationship is hard to get out of, and I don't think the way I did it was right."