Kat Stewart, sister from hell.

On Offspring she plays the abrasive Billie Proudman, half-sister to Nina (Asher Keddie) and on Tangle she play Nat Manning, conceited sister to Allie (Justine Clarke).

But Kat Stewart laughs wryly at the similarities. She loves playing both roles even when it means crossing swords with her co-stars.

“Asher and I have a ball doing those scenes, when we rub each other the wrong way. And working with Justine on Tangle has been an absolute delight too. I feel really bad sometimes as Nat because Allie’s such a beautiful character and so blameless,” she says.

She insists it’s all for the cameras, because she gets along swimmingly with her real siblings, despite not having a sister of her own.

“No, but I’ve got brothers so I guess I get to live that out on screen.”

This season on Offspring, Stewart’s role as Billie Proudman had to be adjusted to accommodate her pregnancy.

“One of the fun things was devising new camera angles and ways to shoot me to conceal my bump,” she explains.

“So I was carrying pizzas, flowers, cushions, talking behind hedges, being shot through flowers, pot plants. It became kind of a game. And lots of big handbags.

“I was about 38 weeks so I was getting pretty enormous by the end and the handbags were getting bigger.”

It was an ironic twist given Billie’s character ended season two trying to get pregnant. But with other characters already expectant, and the maternity hospital setting, writers opted not to weave her pregnancy into the storyline.

With all the talk of babies on the show, perhaps there was something in the water?

“I think Offspring had something to do with it, because Eddie (Perfect) and I both had babies in the last few months, so that tells you something. It was on my mind that I really should get on with it, so being in that headspace with Billie probably gave me the nudge that I needed,” she admits.

“It’s hard to find time for these things and of course there is no time, you just have to do it.

“It’s been mad and intense but I’ve been really lucky because I’ve been able to have the baby at work with me and keep doing what I love.”

But producers also had to give Stewart some time out for the birth of her child, and opted to isolate Billie in New Zealand in scripts, unable to travel home due to a fictional volcanic ash cloud. As a result she spends several episodes only appearing via Skype. That led to new stories for her relationship with Mick (Eddie Perfect).

“She has new opportunities that take her away so he has to work out where they’re at and what’s important to them. I love the way the writers have dealt with it because they haven’t gotten all idealistic and romantic about it,” she says.

“It’s grounded in real life and what real people do and the compromises you have to make when you love someone. So it’s very true to the spirit of their relationship, to date. Passionate but very real.”

Later this year Stewart will join Shaun Micallef in TEN’s new series Mr. & Mrs. Murder. She is also hopeful for more Tangle, but Showtime is yet to confirm a future for the critically-acclaimed drama.

“I would love there to be more. I would jump at the chance to play her again but I don’t know,” she says.

“But to get to do 3 series of anything is a great situation to be in, so I’m very grateful.”

Offspring airs 8:30pm Wednesdays on TEN.