"We had sex!" Lizzie told cameras, before adding: "Explosions!"
She added: "I'm just gonna put it out there. I'm really starting to like Seb. It was really nice to be intimate with him and we're compatible."
Seb echoed her comments, revealing: "We've progressed to the next level. ding, ding, ding!".
The snap comes days after Seb said he felt 'personally attacked' by his mother-in-law, Gillian on last Tuesday night's episode of MAFS.
Gillian told viewers that, "Lizzie is more mature. I think she’s more mature than he is."
She quizzed Seb of having no ambition or drive, and pestered him about having a "savings goal" and no "investment property".
"You’re 31!' she said abruptly. "Why has it taken so long? Lizzie needs a person with reasonable income to sustain the life she’s become a custom to."
"What’s the life she’s a custom to?" Seb asked, adding that she'll have to settle Swarovski over diamonds for the time being, which only infuriated Gillian more.
"You’ll need to earn a lot of money… she’s not cheap. I like stability. I like somebody who knows what they want. I like someone who has a deposit," Gillian told Seb.