Joel, played by Scottish actor Andrew Still, leaves the bad boy stunned in an upcoming episode when he declares that Warren is his father.
A rattled Warren is immediately left to wonder whether Joel is telling the truth or if his arrival is all part of Brendan Brady's revenge scheme against him.
Lomas told TV Times: "Warren's thinking that this kid could be anybody's - he could be making it up or he could be after money. Joel tells him who his mum is and has a picture of her and Warren, but Warren's like, 'Just because she's got a picture of me, it doesn't mean I'm your dad'."
Pictured: Joel, Theresa and Warren.
Mitzeee Minniver (Rachel Shenton) and Theresa McQueen (Jorgie Porter) soon advise Warren that a paternity test is the only way to settle the matter.
Lomas added: "Theresa's like his little sister, and what she says hits home. Warren knows the right thing to do, but he's scared of the truth. If Joel is his son, he's missed out on all these years of his life."
Hollyoaks viewers will see Warren's latest storyline unfold next week.
> Hollyoaks casts mysterious newcomer Joel
> Hollyoaks role was a secret, says newcomer Andrew Still
> Hollyoaks newcomer: 'Joel is a mysterious bad boy'
> Hollyoaks star Jamie Lomas to leave soap
> Read more Hollyoaks spoilers and news