'Game of Thrones' star Hafthor Bjornsson is set to become a father for the first time.

The 31-year-old actor - who starred as Ser Gregor Clegane, also known as 'The Mountain', in the HBO fantasy series - and his wife Kelsey Henson will welcome their first child together when Kelsey gives birth to a baby boy later this year.

Hafthor revealed the happy news on Instagram alongside pictures from his and Kelsey's ''gender reveal'' party, where they both popped a large black balloon filled with blue confetti to signify they are expecting a son.

The star captioned the series of images: ''Swipe right to see gender of the mini me!,'' alongside a shocked emoji.

Hafthor and Kelsey - who are 6ft 9in and 5ft 2in respectively - tied the knot in October 2018 during a ceremony in Iceland, which the actor posted about on Instagram shortly afterwards.

He wrote at the time: ''It is with great pleasure that I now get to call Kelsey Morgan Henson my wife!

I get to hold this beautiful woman through thick and thin for the rest of our lives! I'm so excited for all of the future adventures we will tackle side by side. @kelc33 #justmarried (sic)''

Whilst Kelsey added in her own post: ''Looking forward to pulling this big guy around for the rest of my life.

@thorbjornsson I love you now and forever and promise to stand by your side through all that life throws at us. I love you baby! (sic)''

The professional strongman - who was named the World's Strongest Man in July 2018 - shared a picture of himself effortlessly holding his bride in his arms in a picturesque setting on their big day.

Kelsey posted a photo of the pair holding hands with one another while dressed to impress in their wedding outfits, a bridal gown and suit respectively.