The "Like a Prayer" singer also congratulated Spears on her recent engagement.
Madonna and Britney Spears go way back -- see the infamous lip lock at the 2003 VMAs -- and the "Like a Prayer" singer revealed she still keeps in touch with her pop star pal.
Hitting the red carpet in New York on Thursday for her new concert documentary "Madame X," Madonna said she she rang up Spears earlier in the day to "check in," as she has been a vocal supporter of the "Toxic" hitmaker amid her conservatorship battle.
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View StoryShe told ET she was "just checking in on her, and congratulating her on her marriage. Or her pending marriage."
"I love her," she added.
Speaking with Access Hollywood at the same event, Madonna echoed her sentiment about Britney's engagement to Sam Asghari, saying, "So happy for her, love her to death."
Earlier this month, Britney announced the good news by sharing a clip of her and Sam showing off the sparkler he gave her in an Instagram post, with the caption, "I can't f------ believe it 💍💍💍💍💍💍❣️!!!!!!"
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View StoryAnd back in July, Madonna spoke out in defense of Britney as calls to end Brtiney's conservatorship grew after her blistering court testimony where she claimed it was "abusive."
"Give this woman her life back," Madonna wrote on her IG. "Slavery was abolished so long ago! Death to the greedy patriarchy that has been doing this [to] women for centuries."
"This is a violation of human rights!" she continued, with a final statement for Britney herself: "Britney we coming to get you out of jail!"
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View StoryMeanwhile, Hulu and FX announced that their new documentary "Controlling Britney Spears" will debut on Friday. A press release said the film will take a deep dive into Spears' conservatorship, which -- led by her father Jamie Spears -- has had control over her personal and business life since 2008.
"How the conservatorship has controlled her life has never been revealed," added the statement. "Now, in this New York Times investigation, a portrait emerges of an intense surveillance apparatus that monitored every move she made."
The documentary -- made by the same team behind "Framing Britney Spears" -- features exclusive interviews with individuals who allegedly had "insider knowledge" of the pop star's life under the conservatorship.
Both "Controlling Britney Spears" (which debuts tonight on Hulu and FX) and "Britney vs. Spears (which debuts on Netflix September 28) arrive before the next court hearing in Spears' conservatorship case. On September 29, a judge is expected to hear Britney's request to have Jamie removed from the conservatorship, as well as Jamie's recent petition to end the conservatorship.