Rumors circulated that the trio had fallen out with the 43-year-old but Taboo, real name Jaime Luis Gomez, explained that she turned down the offer to rejoin to focus on her solo album Double Dutchess.
"When we asked Fergie if she wanted to rock with us, she said respectfully, 'I'm going to do the 'Double Dutchess'," he told British newspaper The Sun.
The musician fought off cancer in 2014, and says he and his bandmates decided to reunite without Fergie as he did not want to wait in case his health failed him again.
"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".
Although Jessica fills in for Fergie, real name Stacy Ann Ferguson, Taboo insists it is not a problem as he and his bandmates always felt they were primarily a trio as they started out together.
"When we started the group we were a trio and even when we were a quartet, we were a trio," the 43-year-old said. "Because we are the origins of what we created, it's not foreign at all".
The Black Eyed Peas are to be celebrated with their own British TV special on Saturday, hosted by Joanna Lumley.
Bandleader will, who is pals with the Absolutely Fabulous star, even joked that the veteran actress could join the group for a song.
"We would love to collaborate with Joanna, he gushed. "It would be her as Patsy from 'Ab Fab' in a sketch that turns into a song. It would be a hoot".