"Nothing better than spending time with you," he wrote on the social media platform. "You are an amazing mom & I'm so grateful I get to spend the rest of my life with you & raising our kids. I love you. #HappyMothersDay Weekend my love."
While the message seemed innocent enough, fans of Ciara's ex-fiancé Future took offense with his use of the words "our kids" when referring to her oldest son, Future Jr., 2.
"Step dad …..You can call him your son but you did no work to make that child so try again," one follower wrote, before another added, "Our? Lmaoo."
The couple, who welcomed daughter Sienna two weeks ago, did have some support from fans — with many applauding the Seattle Seahawks quarterback for helping to raise his stepson.
"What's wrong with the man treating his stepson likes his own?" one commenter pointed out. Another wrote, "Do your thang Russell… I love the bond, love, and friendship u have for your wife and kids."
Meanwhile, Future seems to have had a change of heart about Russell's relationship with his son, sending Ciara his own message, thanking the "Goodies" singer for being an amazing mother.
"I appreciate u more than u know, our son is an incredible kid," he wrote. "We made a king, Happy Mothers Day C!"
Previously, the "Mask Off" rapper revealed he was not comfortable with Russell's hands-on approach after photos surfaced of him pushing Future Jr.'s stroller.
"Of course, I don't want no one pushing my son like that's the number one rule, he said on The Breakfast Club. "If I was a kid and my mama had a dude pushing me I would've jumped out the stroller and slapped the s–t out of him."
He continued, "You never do that in our community. You don't even bring a man around your son… you only know this dude a few months and you bringing him around your kid. Who does that?"
Earlier this year, Ciara dropped her $15 million defamation lawsuit against Future.