The Roar hitmaker announced she had played midwife during a visit to a pal's home last Wednesday, taking to Twitter and writing: "Finally you can add 'helps delivers babies in living rooms' to my resume! It's been a miracle of a day... Auntie Katy aka Stylist Auntie."And, in a new interview with Australia's 2DayFM, the singer admits the new mum is her sister.Perry explained: "My sister gave birth in her living room and I got to be kind of like an assistant doula, which, in a home birth, is kind of just there for support."I was in it! I mean I was holding... I probably shouldn't give too many details, but my sister actually is a true rock star. She gave birth in her living room without a single Advil (painkiller)."Besides giving her sibling emotional reinforcement, Perry made sure she documented the entire experience for posterity.She added: "I was kind of like Martin Scorsese, filming everything, you know, getting in there. She doesn't want to see that for, like, a year though."Perry later took to Instagram to post a photo of two pairs of floral sandals, one for an adult and one for a toddler.She added the caption: "One for stylist auntie K and one for baby girl!"