But despite it being her first awards show performance in 15 years, Piers was not impressed.
Speaking on today's Good Morning Britain, he said: "At what point do Cher's outfits become inappropriate? She's 70."
Co-host Susanna Reid said: "Oh yes because you have a cut off don't you? What is it... 59?"
Piers clarified it was 56, before highlighting Cher's silver outfit, which featured draped silver fabric and made it look like the singer was not wearing a bra.
While one breast had a pink heart nipple pasty over it, the other was hidden behind the flesh coloured fabric, and Piers said: "That one in particular, come on Cher for goodness sake love."
But Kate Garraway, who was sitting on the other side of the 52-year-old, replied: "She's on stage! It's not like she's in the supermarket, it's different rules surely?"
Never one to back down, Piers continued: "She's a grandmother, it's like for goodness sake put it away, grow old gracefully, put them away."
Susanna and Kate both felt Cher was ageing "beautifully", but their co-host retorted: "I think her [plastic] surgeon's probably working over time."
When Susanna insisted she looked great at the Billboard Awards, Piers questioned her if she really believed what she was saying, adding: "You don't think 'toe-curling' 'cringing'... are you going to be doing that when you're 70?"
Susanna replied: "If I look like Cher..."
Having the final word, he said: "What happened to just being dignified in this country? Seriously."
But karma came quickly to Piers, as he got so animated about the situation he ended up spilling his hot tea on his leg.
As he gestured, the liquid jumped out of his mug, leading him to jump and Susanna look shocked.
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