The rumor was confirmed. In an interview with Billboard, Questlove explained the collaboration with Elvis Costello.
Originally the two musical acts wanted to collaborate on a few songs. However, the few songs grew to “13 or 14″ songs that the team loved, out of the 20 that they created.
Questlove had seen Costello perform on Late Night several times. After each performance they wanted to work together more.
“It was really love at first sight. The second time he came on, we surpassed the first one. So by the third time, he was like, ‘Let’s stop messing around and do something together.’”
They are planning to head back to the studio soon to mix and master the album. They have not decided whether to release through Elvis’ team or through Def Jam’s team.