United Kingdom, July 21 -- Robbie Williams has sarcastically apologised to spilling a mint during a live TV interview.

The chart-topping singer has laughed off online speculation about his sobriety, after a white substance was seen falling from his mouth during an interview with MagentaTV at the World Cup final in New Jersey.

Robbie, 52 - who performed the World Cup anthem Desire with Nicole Scherzinger and Laura Pausini during the closing ceremony - said on Instagram: "Just like to apologise for the object that fell onto the microphone yesterday.

"I was deeply unprofessional, and people are worried about me, but it's okay 'cause I have several more."

Robbie - who has previously been open about his sobriety journey - captioned the pos...