The youngest of the Jenner-Kardashian clan, Kylie is said to have dumped the rapper over "something he did".
TMZ says that the split was "sudden and nasty".
According to sources speaking to the showbiz website, Kylie and Tyga split on Thursday (19 November), just after Kylie returned from Australia.
One source said: "It's something Tyga did."
Another says "pressure from the Kardashians" was to blame.
People report that Kylie is "fuming" with Tyga, after he had "broken her trust".
And, even worse, Thursday just happened to be Tyga's 26th birthday.
As if proving the reports, Kylie did NOT attend Tyga's birthday party at The Nice Guy and 1 OAK in West Hollywood. And nor did she - or any of her family - send him birthday wishes on social media.
For Kylie's 18th birthday earlier this year, the father-of-one bought her a white Ferrari.
The couple only went public with their romance after she turned 18 in August, after months of speculation.
They had even discussed getting engaged and eventually married.
Earlier this week, Kylie told fans she's a relationship girl.
In a post to her official Kylie Jenner App, she explained: "I've never believed in the idea of the public knowing everything about my relationship and every time I break up and make up. I'm not afraid to show who I'm dating, but I'm also not about to talk about every little detail of my relationship.
"Everyone who knows me, knows I've always been a relationship girl. I've never believed in the idea of casual dating or being with two people at once. I feel like I only have room for one person in my heart and I want to give whoever I'm with all the attention they deserve."
All you need to know about Kylie Jenner:
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