"An ode to the joy of multilateralism," Schinas tweeted posting the photo depicting Juncker sitting at a grand piano and playing something.
The EU official anthem is based on famous "Ode to Joy" composed by Ludwig van Beethoven in 1823.
The two-day G20 summit kicked off in Japan's Osaka on Friday. The participants are discussing a wide range of issues, including global security, trade relations and global terrorism.