The pair, who play Walford's Lauren Branning and Tyler Moon, started dating last year after they began working together on the BBC soap.
However, Jossa has now told The Sun's TV Buzz magazine that she first met Discipline before he had landed his EastEnders role.
Jossa explained: "It was at my favourite nightclub. Tony came up and said he was auditioning for EastEnders. I didn't believe him, though when I walked back to my mates, I was like, 'Did you see his teeth?! He's well fit!'
"But I left it. I didn't think he was going to join EastEnders. He even added me on Facebook and I deleted him! Then a couple of months later, I came into work and there he was. I called my cousin and said, 'Do you remember Fit Boy? He is in the building'."
She continued: "We didn't get together for ages, as we thought it'd be weird on set, but it got to the point where there was no other option.
"We kept it a secret at first, but everyone was like, 'Oh, we knew'. Tony is very romantic - he got me a teddy bear for our two-week anniversary. But we're not cheesy, we find the same things funny and that's important."
"It still all feels ridiculous," she said. "My mum's put the NTA award on the mantelpiece. But it's not sunk in yet."
Jossa's full interview appears in the next issue of TV Buzz magazine, which is free in The Sun tomorrow (March 17).
> EastEnders Moon actors confirm co-star romances
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