The Manchester City playmaker levelled up the scoring in the Champions League semi-final first leg - which ended 1-1 - with a scorching 67th-minute strike.
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Pep Guardiola's side were trailing after Vinicius Jr's long-range effort in the first half, with De Bruyne then scoring from an almost identical spot.
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His first-time effort from outside the box arrowed into the bottom left corner to spark wild celebrations from the City squad and travelling fans.
But the goal infuriated Ancelotti, who believed it shouldn't have stood.
De Bruyne looked to have fouled Toni Kroos moments before his thunderbolt, while there also shouts for a possible handball on John Stones and throw-in appeals after Bernardo Silva appeared to have hooked the ball back-in from over the touchline.
The former Everton manager angrily protested on the sidelines, with midfielder Luka Modric also in disbelief at the equaliser being allowed to stand.
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Ancelotti's animated antics saw him booked by match official Dias, which only further riled up the Real faithful.
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Though Ancelotti declared he didn't know why he was cautioned, as he told BT Sport: "I don't know why.
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"I was not on the pitch. I think he could give a yellow card to the player not the manager."
Speaking on talkSPORT commentary, England legend Stuart Pearce stated that the former Chelsea manager can have no complaints over De Bruyne's goal.
He said: "If he was to see the replay again, I think he would have a different opinion.
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"I think Modric is complaining about the potential handball from John Stones earlier by the way he is pointing.
"It skimmed his hand, but you can't get out of the way of it. It's physically impossible."
There was also drama at the end of the first half when Jack Grealish was shoved by Dani Carvajal into the advertising board.
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The England international was left in a heap and reacted to Carvajal, who went down holding his face, even though the City star hit him on the arm.
And on the stroke of half-time, Madrid's midfield maestro Kroos was cautioned for a wild hack on Ilkay Gundogan.
Pearce was of the opinion that the German should have been given his matching orders, as he remarked: "That is a sending off challenge from Kroos."
Adrian Durham then stated on air: "That's a clear red card. This is outrageously bad refereeing and this could cost Man City."
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Both teams will face each other at the Etihad next week, where the winner will face either Inter or AC Milan in the final on June 10.