Kendall Jenner is ''serious'' about Blake Griffin.

The 'Keeping Up With The Kardashians' star has been growing close to the basketball player and whilst they started off in a more ''casual'' romance, things are said to be heating up between the pair.

A source told People magazine: ''Kendall was in a great mood [at her party]. She and Blake hung out, but they also mingled separately ...

''Kendall is very happy with Blake. They started out more like friends, and then it was very casual. But it seems more serious lately. When they are not together, they keep in touch over the phone. Her family has accepted Blake. They are spending time getting to know him.''

It had previously been claimed that Kendall was enjoying ''playing the field'' by going on dates with Blake while still talking to her ex-boyfriend rapper A$AP Rocky, who she dated briefly last year.

An insider said at the time: ''Kendall and Blake have been hanging out quite a bit and are having a good time. They met in passing a few times and hit it off. She's still talking to Rocky as well. But he isn't the type to settle down or be a good boyfriend, so she's playing the field too. She's seeing Blake romantically. It's nothing serious. She has been in LA a lot lately, and is having fun.

''Work will soon take over her life again, so who knows what will happen will Blake then. She is having fun right now and that's all that matters to her. She takes her career very seriously and that's her number one priority right now. Kendall is keeping her options open. She's still dating A$AP Rocky as well, but she and Blake are hanging out, and there's potential there.''