Kourtney Kardashian and long-term boyfriend Scott Disick already have two children, Mason, 4, and Penelope, 23 months, but it seems as if they are expecting a third son or daughter this December.

The reality star confirmed she is expecting during a premiere episode of Keeping Up With The Kardashians on E! last night, which saw the brunette beauty, 35, tell Scott the exciting news.

She said: "I'm pregnant… It was not a plan."

The announcement was saved for the end of the episode in a montage of clips showing viewers what would be coming up on the reality show later on in the season.

Viewers had a hint that Kourtney would be addressing pregnancy rumours in the episode, as sister Kim - who recently married Kanye West - teased them on Twitter a few hours before.

She wrote on Twitter: ''Kourtney will also be addressing pregnancy rumours this Sunday on our premiere!,'' adding ''So be sure to tune in! #keepingupwiththeKardashians. (sic)''

Kourtney and Scott, 31, have been together since 2007 and their relationship's many ups and downs have been documented on Keeping Up With The Kardashians for years - including the birth of son Mason.

We wonder if the star, who is reportedly "only a few months along", is expecting a boy or a girl?