The Kardashians welcome a new addition – on a very special day!

It was a big day for the Kardashian family yesterday, as big sister Kourtney welcomed a baby boy.

The star gave birth to the little one yesterday afternoon, her third child with Scott Disick.

The couple already have two children together, two-year-old Penelope and five-year-old Mason. And to make the new arrival even more special, yesterday also happened to be little Mason's fifth birthday. A pretty cool present if you ask us – though we're not sure Mason would agree!

Although Kourtney did not officially announce the birth on social media, she did share some sweet updates throughout the day, including this picture of one of Penelope's dolls in the new baby's cot, with the caption, "Nap time! Someone's already using our new crib."

Auntie Kim made sure Mason wasn't feeling left out on his big day by organising a special family trip to Disney On Ice at the Staples Centre in Los Angeles. Penelope and Mason were joined by Kim's one-year-old tot North West, and Zeplin Black, the adorable son of make-up artist Joyce Bonnelli.

Kim shared this cute snap on Instagram of the foursome:

Just look at those outfits! We're loving North and Penelope in their Doc Martens.

Congratulations to the growing Kardashian family!