Is she an auntie or a stepmom? Tyga's girlfriend Kylie Jenner babysits King Cairo after Blac Chyna gave birth to daughter Dream

Kylie Jenner played stepmom to boyfriend Tyga's son King Cairo on Thursday.

The 19-year-old reality star watched over the four-year-old boy after his little sister Dream was born to her rapper beau's ex, Blac Chyna and brother Rob Kardashian.

She put on an eye-popping display as she nearly spilled out of a plunging dress while carrying the four-year-old little boy. 

Stepping in as stepmom! Kylie Jenner looked after King Cairo on Thursday after the birth of his little sister, Dream, on Thursday

Slink around in a slip dress by Nili Lotan

Thanks to the revival of all things 1990s (chokers, checked shirts, bodysuits) the humble slip dress has also made a return.

And this is one comeback we can get on board with. Back in the day we used to wear them with a T-shirt layered underneath, a pair of Dr Marten boots, with a flannel shirt tied around our waists.

In 2016, however, they're being styled with sneakers à la Kylie Jenner who was spotted out and about in this navy silk version by Nili Lotan, a label beloved by Gigi Hadid, Kendall Jenner and Chrissy Teigen to name a few.

So why not get on board with this trend? A slip dress is perfect for a slinky party season option or on chilly days add tights and a long sleeve tee. Kylie's dress is no longer available in blue but click (right) to shop the other shades in the same style now.

Or stick to seasonal navy with our edit below.

* PRICES MAY NOT BE AS ADVERTISED

The Keeping Up With the Kardashians star left little to the imagination in the low-cut navy satin frock.

Her ample bosom was on display in the slinky number which was held up by two thin spaghetti straps.

She wore her platinum blonde locks styled straight with the ends curled and parted to one side.

Eye-popping! The 19-year-old reality star nearly spilled out of a plunging dress while carrying the four-year-old little boy

Family affair: The Keeping Up With the Kardashians star played the picture perfect stepmom to her beau Tyga's son - who is also the child of her brother's fiancée Blac Chyna

'Beyond beautiful': Kylie gushed over her niece, which is also the sister of her boyfriend, Tyga's son

It's a girl! Dream Renée Kardashian arrived on Thursday morning at Cedars-Sinai hospital in Beverly Hills

Authors: Kylie and her sister Kendall announced a new book

Kylie became an aunt to Dream as her 29-year-old brother Rob and his fiancée Blac, 28, welcomed their first child together at Cedars-Sinai hospital in Beverly Hills.

Blac and Tyga, 26, started dating in November 2011 and welcomed their son Cairo in October 2012.

They confirmed their engagement in December 2012 but ultimately split in 2014. 

The video vixen and Rob announced their engagement via Instagram in April after three months of dating. 

Loved up: The brunette beauty and father-of-one are thought to have started dating in 2014 but they didn't go public with their romance until late 2015

While things were originally somewhat complicated, drama surrounding the Kylie Lip Kit entrepreneur and the mother-of-one had reportedly been quashed months ago.

Back in September, Rob and his wife-to-be insisted that the families are were 'super comfortable' with each other, after having talked it out.

'We're not holding grudges,' Blac told People magazine, explaining: 'We've all talked, I've met up with Kylie. Everybody is mature... We've moved on.'  

Getting along: Blac reportedly worked things out with love rival Kylie, saying the pair (who shared this friendly snap back in April) had talked things out, according to People

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