They released their duet, Hold Me Closer, on Friday, marking her first new music in six years and her first release since the end of her 13-year conservatorship.
The track mixes Sir Elton’s 1971 hit Tiny Dancer with his 1992 song The One, while parts of Don’t Go Breaking My Heart from 1976 also feature in the song.
Spears shared a video from her bath tub to Twitter after appearing to delete her Instagram account earlier in the day.
She said: “Hello Sir Elton John, we are like number one in 40 countries. Holy shit. I am in the tub right now and I am about to go and have the best day ever, and I hope you are well.”
Replying on his Instagram page, Sir Elton said: “Hey Britney!! Thank you for this message. You’ve made my day!! Hope everyone has the best day dancing to our song!”
Later Spears posted a video of herself heading out for the day wearing a stylish white coat with black trim, a wide-brimmed hat and large sunglasses.
She captioned the clip: “Keep smiling folks … KEEP SMILING !!! Psss I LOVE YOU ALL !!!”
Hold Me Closer comes after the end of Spears’ conservatorship which allowed her father Jamie to control her freedom and finances.
The song also follows the success of Sir Elton’s collaboration with Dua Lipa on their track Cold Heart (Pnau Remix), released last year as the lead single from Sir Elton’s 32nd studio album, titled The Lockdown Sessions.
In June this year Spears married her long-time partner Sam Asghari at her home in Los Angeles at a ceremony which included high-profile celebrity guests including Madonna, Donatella Versace, Paris Hilton, Selena Gomez and Drew Barrymore.
Spears wore a custom Versace off-the-shoulder wedding dress.