Atalanta's 1-1 draw with Sassuolo was enough to secure the Serie A title with four games to spare for Antonio Conte's side. And Lukaku took to social media to aim a shot at his old rival.
The pair clashed heads during a fiesty Milan derby, with the Belgian allegedly calling his former Manchester United teammate "a son of a b***h" before saying "f**k you and your wife" towards the Swede. They then butted heads and exchanged insults in the Coppa Italia quarter final tie earlier this year.
Lukaku wrote on Twitter: "The real god has crowned the king! Now bow down. King of Milano," the striker added, with a winking face and a crown emoji.
Lukaku has already called the 2020-21 season the best season of his career as he scored 21 goals in 33 Serie A games to drive Conte's men to the championship.
He said: “Last year was good too, but this was the best of my career. It’s wonderful and I hope to continue like this. I want to thank everyone, I am truly so happy. I am so happy for all the Inter fans in the world, for the team, the staff, the President and everyone."
Lukaku concluded, “It was a wonderful year for us, I am truly proud to play for Inter. I wanted to come out here and celebrate along with the people. I told my friend this was the best way to experience it, to be there with the fans. For me and many of my teammates, this is our first league title, so it’s a moment we wanted to share with them.”