A source tells ET that Vanderpump, 58, had just landed in Los Angeles from Las Vegas on Sunday evening, where she was working on her new Vanderpump Cocktail Garden, when Gaga reached out asking her to get together. According to the source, Vanderpump rallied and met Gaga, 32, for dinner at Pump in West Hollywood, where they were spotted in a corner area near the restaurant's front bar around 11 p.m. by a second source.
“They even did some guest DJing together,” the first source says.
“They were both sipping drinks and dancing! They are quite the duo!” the second source adds.
The second source notes that Vanderpump’s husband, Ken Todd, and Vanderpump Rules cast members Tom Sandoval and Billie Lee were also there. “They were all in good spirits and very friendly,” the source says.
After dinner, the first source says Vanderpump wanted to show Gaga her newest West Hollywood spot, Tom Tom. The source says the two hung out in the garden at Tom Tom into the wee hours of Monday morning.
ET’s first source says Vanderpump, who’s normally a morning person, slept in late Monday after her evening with Gaga.
Vanderpump took to Twitter on Monday to call her night out with Gaga "sooooo fun," adding the hashtags "#NaughtyChildren" and "#NoPress" alongside a crying laughing Bitmoji.
Vanderpump has taken to social media as of late to share a behind-the-scenes look at her new Vanderpump Cocktail Garden, which is set to open at Caesars Palace in Las Vegas on April 1. In one video, fans see the restaurant in the construction phase, while the reality star praises industrial designer Nick Alain for his work on the space.
Another clip shows part of Vanderpump's busy time in Vegas -- just one day before her big night out with Gaga -- where 3,000 people turned out to celebrate the upcoming opening of her newest venture, an experience Vanderpump called "incredible."
Prior to meeting up with Vanderpump on Sunday, Gaga stunned in Rodarte at the Daily Front Row's 5th Annual Fashion Los Angeles Awards, where she presented an award to her hair stylist, Frederic Aspiras.