The 'Where Is The Love?' star - who marked four years since he overcame the disease on Monday (10.09.18) - admitted it was his family and bandmates who inspired him to stay strong during his fight with the illness.
Appearing on ITV's 'This Morning', he said: ''It was brutal - it was like nightmare, torture and war. But the thing that kept be fighting on was my wife and my kids, and knowing that I could be on that big stage again with my best friends.''
The 43-year-old rapper appeared on the British daytime show with Will.i.am, and he admitted the longtime friends became even closer together.
He explained: ''The experience of me battling cancer brought us closer as friends before anything. You see on stage, Black Eyed Peas - it's a friendship, a brotherhood that started since we were teenagers.''
'The Voice' judge will.i.am also revealed his excitement at getting back together with the group - who will return to the UK on tour next month - after spending too much time alone on the road.
He said: ''Dude, I don't like being up here alone, I miss my best friends. I didn't sign up to be a solo act, I signed up to be in a group. We're best friends.''
The reunion for the 'I Gotta Feeling' rappers - who are celebrating their 20th anniversary in 2018 - was kick-started back in 2016 when will.i.am reformed with Apl.de.ap and Taboo for a concert at the Royal Albert Hall in London in May 2016, the first time the trio had performed together in five years.