With 20-minutes till kick off, the opening ceremony ended with Ronaldo (the original, Brazilian version) joining Robbie and Aida.
Ronaldo dummied the opening kick, allowing a child to pass the ball to mascot Zabivaka.
Videos and pictures started to circulate on social media of Williams with his middle finger up at the camera shortly afterwards.
English pop star Robbie Williams, former Brazil striker Ronaldo - scorer of 15 goals over three tournaments - and Russian Federation soprano Aida Garifullina were the star attractions at Moscow's Luzhniki Stadium before the opening match of Russian Federation 2018 kicked off.
Before the game, Russian President Vladimir Putin addressed the fans and players, saying: "Russians love football, it is what we call love at first sight, ever since the first official match was held in the country in 1897".
There will also be performances by the legendary Spanish Tenor and Opera Icon Placido Domingo followed up by his fellow opera singer and Peruvian Tenor, Juan Diego Florez.
The 2018 World Cup begins today, but while many are waiting for the games to begin, others are looking forward to the opening ceremony.
Although opening ceremonies can sometimes be long and drawn out-see World Cup 1994 in the United States-hosts Russian Federation proved there is a way to begin festivities swiftly.
Singing a slew of his hits, Williams turned directly to the camera during his performance of "Rock DJ", clearly changing the lyrics to "I did this for free" before lifting up his finger. "As it was broadcast live, we did not know what would happen during Robbie Williams' performance and we apologize". The Guardian reported that he had said he was "happy and excited" and to perform at the opening, and that it was the "fulfillment of a boyhood dream".