Khloe Kardashian says the ''worst part'' of her pregnancy so far has been keeping it a secret from her family.

The 'Keeping Up With The Kardashians' star waited to tell her relatives the happy news she is expecting a baby with her partner Tristan Thompson but admits it was tough keeping it a secret until their big announcement.

She wrote on her official website: ''Even though expecting a baby is SO exciting, the first trimester can be the worst. The worst part was keeping this major secret from my family, though! I'm with my sisters pretty much every single day, so it was hard to not be able to say why I was so sick or couldn't do certain things.

''We wanted to tell everybody at one time, which made things even more tricky - how do you get all those people together in one room?! - but it was so amazing when we finally did! Keeping the secret from the outside world wasn't as big of a deal for me. I believe there are certain things that need to be held private and for yourself. It was beautiful to have something that was just ours. (sic)''

It comes after Khloe admitted her pregnancy is ''physically and mentally trying'' but praised sportsman Tristan for making everything ''as easy and beautiful as it can be'' during the nine months.

She said: ''Having a partner that is equally as excited as you are, and is such a support system, is crucial! Tristan has been an angel to me! This process is trying - physically and mentally - but Tristan has made everything as easy and beautiful as it can be! More than I could have imagined.''