By Lisa Respers France, CNN

(CNN) -- John Mayer is well known for his romances, but Andy Cohen is not one of them.

The singer celebrated his friend's 50th birthday on Sunday's episode of "Watch What Happens Live With Andy Cohen" on Bravo.

Mayer serenaded Cohen with his rendition of "It's My House" by one of Cohen's favorite artists, Diana Ross.

"Best birthday ever," Cohen said afterward, giving Mayer a kiss on the lips.

Mayer admitted that he learned the song just for his friend.

"I have done nothing but learn that song in the last 48 hours," he said. "I have ate, breathed and slept 'It's My House,' and I am now a fan of that song!"

Mayer hosted the after show and joked about how Cohen's high-profile friends would not want to be around the singer were it not for Cohen being his friend.

"If you are someone who cares about your image...dating John Mayer at this point is conceptually just sort of a no-no," Mayer said. "So it's really fun to get to hang out with your friends, your A-list star friends, who otherwise would be highly uncomfortable sitting around me."

While discussing Mayer's low tolerance for drugs, the singer said "I know my body," which caused Cohen to quip "I feel like I know your body, too."

"Do you think people wonder if we're in a secret relationship?" Mayer asked Cohen.

"All my team does," Cohen said, after turning to see his staff nodding in agreement on set.

For the record, the pair's friendship is well-documented on social media.

"I love you, and you are such a special person that I'm sure you are known throughout the universe," Mayer wrote in one caption of a photo of the pair in which he joked about crafting a birthday message to Cohen.