The actor landed the role of Walford's Joe Wicks when he was 16 and played the character for nearly two years in 1996 and 1997.
However, Nicholls - now 32 - told PA: "I can't really remember it. It's really weird. I remember driving to work and being on set a few times, but if I ever look back now, it's just blank.
"I just can't really remember being in it. I do recall coming out of EastEnders and the attention dying down 50% in the first six months, and then a couple of years later it was 95%."
EastEnders fans recently saw Joe's father David (Michael French) return to Albert Square for a short return stint tying in with Pat Evans's emotional exit storyline.
Meanwhile, Nicholls is now starring in ITV1's Law & Order: UK, playing DS Sam Casey.
> Paul Nicholls Law & Order: UK Q&A: 'Sam is a no-nonsense copper'
> Read more EastEnders news and spoilers