The jaw-dropping cost of Aryna Sabalenka's 12-carat engagement ring revealed

Aryna Sabalenka may be a superstar on the tennis court, but she's being outshone today by her massive engagement ring.

Sabalenka and her boyfriend of almost two years, Georgios Franguli, are now engaged -and it's clear Franguli spared no cost on the 12-carat ring.

The ring, which was custom-made for the world number one tennis star, was designed by US-based jeweller Isabela Grutman and Franguli over a number of months.

Watch the video above.

Diamond expert Nick Ireland told nine.com.au the ring is worth an estimated $US1 million ($1.4 million).

Ireland said a similar diamond of flawless clarity would fetch a little over $2 million in the Australian market.

"The main diamond is 12-carats, then you have possibly up to a carat of diamonds on the band itself," Ireland said.

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"Obviously, if it's a natural diamond of high colour and high clarity, it could easily be more than a $US1 million... reaching up to $US1.5 million."

The ring features a hidden halo encrusted with emeralds, which is the tennis star's birthstone.

"Having emeralds in a little hidden halo underneath ... you wouldn't just see that sort of combination," Ireland said.  

"It certainly wouldn't just be sitting there on the shelf ready to go.

"The emeralds are only about 1.5mm in size maximum, they're not [worth] a huge amount, but they appear to be very high quality, very high colour.

"It's a nice personal touch."

In an interview with People, Grutman said the emerald halo was Franguli's idea.

"It's a personal touch that makes the ring uniquely hers," she told the outlet.

Grutman took to Instagram to explain exactly how she came up with the personalised design for the tennis world number one.

"I'm creating a very special ring for a very special person, and I'm so excited about it," she said in an Instagram video.

"I'm analysing this 12-carat oval diamond ... When I have the future husband pick the perfect ring and stones, I analyse what she likes.

"Is she more modern? Is she more classic? What is her personality?"

"This stone is perfect for this woman I'm designing for."

The video also shows more details of the ring up close, including the hidden halo and the claws holding the diamond in place, which are also encrusted with diamonds.

While the regular person can't afford to drop $2 million on such a massive stone, Ireland said a 12-carat lab-grown diamond is worth about $15,000 to $20,000.

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