Kourtney Kardashian has given birth to a baby boy.

The 'Keeping Up With The Kardashians' star and partner Scott Disick have welcomed their new arrival on the 5th birthday of their eldest son, Mason.

The 35-year-old television personality - who also has Penelope, 2 - is believed to be incredibly excited about the new addition to the family.

A source told E! News: ''The family is freaking out with joy. What an amazing coincidence.''

Earlier, Kourtney shared a photo of Mason, calling him the ''coolest little boy''.

She wrote: ''Happy birthday to the coolest little boy in the entire world. You teach me so much every single day and changed my universe the second I met you.

''You have taught me what life is all about and I am truly blessed and honored to be your mommy. (sic)''

Meanwhile, Kourtney recently posed nude for DuJour magazine whilst nine months pregnant, something which she found ''wonderful''.

Speaking about the shoot, she said: ''I had done a nude shoot when I was pregnant with Mason, really last minute just for myself, and I love it.

''This time, we were shooting for our show, and everyone on our camera crew was like, 'You are so comfortable just walking around naked and pregnant!'

''[But] what appeals to me is celebrating the shape of my body being pregnant and capturing that time in my life ... It's a wonderful thing to be able to show my children these photographs one day and say, 'This was you inside' ... I'm at my best when I'm pregnant.

''It's such an amazing feeling, the transformation that your body goes through. There's something about that that's so empowering and beautiful.''

Kourtney Kardashian has named her third child Reign Aston Disick.

The reality TV star gave birth to the latest member of her family on December 14 and there has been much speculation surrounding the name of her baby boy ever since.

But Kourtney, 35, has ended the rumours by confirming the baby's name on Instagram.

She wrote: ''Madly in love with my little Reign Aston Disick.''

Reign's name is English in origin and means sovereign or ruler, but it remains to be seen whether the decision of Kourtney and her partner Scott Disick leads to it becoming more popular among the US public, as was the case with their eldest son Mason, who was born exactly five years earlier.

Whoa, that's pretty cool how he was born on his oldest brother's birthday.