The couple spent the singer's birthday weekend ringside at the Mayweather-McGregor fight and with family.
The hip-hop mogul, along with his sons and entourage, surprised his girlfriend with a cake and a sweet birthday serenade to kick off the day.
The three Combs fellas sang the Stevie Wonder rendition of "Happy Birthday" to Cassie and even included some smooth dance moves to go along with the surprise serenade.
Although the day was supposed to be about the birthday girl, Diddy couldn't resist jokingly calling her out for the brand of water she was drinking.
"Didn't I teach you how to be brand loyal?" he asked after giving her birthday wishes. Diddy is referring to the fact that he recently partnered with Mark Wahlberg to launch a new line of electrolyte heavy water called AQUAhydrate water.
The couple brought in Cassie's birthday in Las Vegas, just in time for the big Mayweather vs. McGregor boxing match. Diddy and Cassie showed up and showed out during fight night that turned into a special date night for them.
Now that's how you do Vegas for your birthday!