Watch: Billionaire bidder Adrian Portelli makes a shock announcement as House 5's secret buyer is revealed

It was a bidders' war as Kristian and Mimi's house went under the hammer, but in the end a mysterious buyer snapped it up on Auction Day.

A buyers' advocate offered a whopping $2,930,000, making Kristian and Mimi instant millionaires.

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But who was the secret buyer behind the paddle?

In a shocking twist, the secret buyer revealed themselves – and was in fact in the room the whole time.

Yep, it was none other than billionaire bidder Adrian Portelli who in the video above, had some huge news to announce.

Catch Adrian's big announcement in the video above.

"We got the royal flush!" Adrian revealed just moments after the final auction, with his little boy in his arms. "We bought all five houses."

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Although we didn't see Adrian bidding during House 5's auction, Adrian revealed he had a secret...

"All the contestants were playing the game, so I thought I'd play the game back," he revealed and there was a massive reason why.

"That was my last appearance on The Block and I thought I'd go out with a bang," he smiled.

"Thanks for having me, it's been fun."

WATCH: Kylie and Brad share their relationship status ahead of their grand Auction Day return

Adrian's big announcement came as a surprise and you can catch everything he had to say in the video above.

And just like that, The Block's mammoth 20th season is officially done and dusted!

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