Novak shared the happy news with fans via Twitter on Thursday (24 April), alongside a sweet picture of the couple smiling at each other.
Novak wrote: "Jelena is pregnant! We will be parents soon! #blessed."
He later added: "Thank you all sooo much for the compliments. We love you and can't wait to see "little one" soon."
Jelena added: "We will grow this family by 1 very special member this year :) Keep spreading love&joy& #GoodNews."
Novak, 26, made the announcement while in Athens with Jelena. He's been taking a break from playing while recovering from a wrist injury.
World Number Two Novak and Jelena became engaged in September 2014 after eight years of dating.
Jelena is a familiar figure to tennis fans as she's often seen courtside supporting Novak. She's also the director of his charitable foundation, founded in 2007, which supports disadvantaged children in Novak's home country of Serbia.
Last year, Novak paid tribute to his girlfriend at a gala dinner held in London, saying: "Love is the greatest driving force in my life, it can create miracles."
Congrats to Novak and Jelena!
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