Emma co-hosted the BBC show alongside radio presenter Nick Grimshaw today.
Lucy Benjamin was one of their guests ahead of her big return to EastEnders which is set to air next week.
Things are set to kick off in Albert Square as multiple storylines come to a head and her character Lisa Fowler reappears.
Conversation turned to Lisa’s iconic storyline when she was unveiled as the perpetrator in the Who Shot Phil? mystery.
However, when joking about revealing the culprit to viewers, Emma accidentally said it was Lucy who shot Phil, not the character.
Emma began: “In 2001, 22 million people tuned in to find out who shot Phil, and I have a little spoiler for you, it was Lucy.”
“It was Lucy. If you were saving that to watch, it was Lucy,” Nick chimed in.
“Or Lisa,” Emma quickly added.
Lucy then chimed in: “Lisa. It wasn’t actually me.”
“Not actually Lucy,” Emma corrected.
Lucy went on to discuss her return storyline as her character is set to return to help out daughter Louise Mitchell (Tilly Keeper) but soon gets caught up in Mel Owen’s (Tamzin Outhwaite) son Hunter’s (Charlie Winter) plan.
As fans will know, Lisa and Mel were best friends during their heyday on the programme.
“She comes back to get Keanu and Louise to leave the country but then she gets embroiled in Hunter’s revenge plan that happens and she doesn’t get to leave and drama unfolds,” Lucy explained.
Lucy left the show in 2003 but has since returned for guest stints.
She’s not the only Walford icon returning to the Square as Bianca Butcher (Patsy Palmer) is making a comeback too for the eventful week.
Lucy reflected on being back in the fold with the cast among the old and new faces.
The actress shared: “It’s just lovely seeing the old faces, and the new ones there. Great kids are there doing fabulous stuff now.
“It’s like going home. It’s just amazing. I mean I was back a couple of years ago but for a very short stint.
“You just settle in to things so easily and it’s like it was only yesterday and it was 16, 17 years ago when I was there properly.”
The One Show continues Monday at 7pm on BBC One while EastEnders continues Monday at 8pm on BBC One.