The 'Where Is The Love?' singer didn't rejoin the rest of the group for their comeback earlier this year, and Will.i.am has insisted it wasn't a difficult transition going back to the original lineup with taboo and APL.DE.AP.
Speaking to The Sun newspaper's Bizarre column, he said: ''Returning to the trio that we were wasn't something which felt jarring or foreign to us.
''When we started the group we were a trio and even when we were a quartet, we were a trio. Because we are the origins of what we created, it's not foreign at all.''
Fergie joined the group in 2002, with the group first getting together 12 years earlier.
The star was offered the chance to join the reunion, but wanted to focus on her 2017 album 'Double Dutchess', and Taboo didn't want to wait after his battle with testicular cancer in 2014.
He explained: ''When I beat cancer I felt rejuvenated, like I wanted to be back on stage again.
''When we asked Fergie if she wanted to rock with us, she said respectfully, 'I'm going to do the 'Double Duchess''.
''And I felt like time waits for no man, so we went in to create the album 'Masters of The Sun Vol. 1', knowing we had to go back to celebrating the accomplishments of us being a trio.''
She has since been replaced by 'The Voice Philippines' finalist Jessica Reynoso, who joined the group for a special 20th anniversary performance.
'20 Years of the Black Eyed Peas' will air on ITV on Saturday night (22.12.18) at 10pm.
His new album Underneath It All is out now.