Tim McGraw has marked the 21st anniversary of 9/11 with a touching tribute to the emergency services posted on Instagram. MORE: Celebrities mark respect for 9/11 with powerful tributes: Kelly Ripa, Tom Brady & moreTaking to the social media platform on Sunday, the country music singer posted a photo from the aftermath of the event, which sees three firefighters comforting each other. WATCH: The true story behind how Tim McGraw and Faith Hill fell in loveHe added the caption: "Today we honor the memory of those who were lost on #September11, and thank all of the first responders who put their fellow Americans first and ran towards danger to save and protect.