British synth-pop duo Pet Shop Boys have revealed the artist they most regret not collaborating with during their 40 year career.

Forming in 1981, lead vocalist Neil Tennant and keyboardist Chris Lowe, who were named the most successful duo in UK music history in the 1999 edition of The Guinness Book of Records, have worked with the likes of Robbie Williams, Madonna, Girls Aloud and Liza Minnelli.

This past weekend, the duo spoke at The Guardian Live “An evening with Pet Shop Boys” event in London on April 22, and disclosed their regret at never working with the legendary Nina Simone.