Attending the filming of the first BGT auditions of the year, the 48-year-old modelled an aquamarine cocktail dress, complete with a ruffled neckline and short sleeves.
Designed by London Fashion Week designer Edeline Lee, the figure-hugging gown draped elegantly around her curves.
Sharing a snap with her Instagram followers, the mum-of-two showed off her toned pins in a pair of chic cream stiletto heels.
A pair of tinted shades topped off the outfit, as she enhanced her natural beauty with barely-there makeup.
In the comments underneath, Amanda's celeb pals and fans alike weighed in on the sophisticated look, piling on the compliments.
Coronation Street's Catherine Tyldesley said: "Gorgeous!"
Pussycat Doll Ashley Roberts added: "Well she purrrrdy."
While a third fan chipped in: "You look amazing. Colour is perfect on you."
Amanda arrived at the venue in a £225,000 Aston Martin, lying on top of the bonnet for pictures before heading inside the Lowey Theatre.
Last year, veteran Colin Thackery stole the judges' hearts and was crowned the BGT winner.
The chuffed 89-year-old was awarded £250,000 and the opportunity to perform at the Royal Variety Performance before the Queen.
After his win, he announced: "[I am] astonished. I don't know what to say. I'm stuck for words for a change."
The BGT outing comes after Amanda was warned to toe the line by show bosses this week.
A source told Daily Star Online BGT bosses are keen to avoid a repeat of last year's antics which saw the whole of The Lowry theatre evacuated after Amanda and Simon tried - and failed - to cook beans on toast in the venue's kitchens.
The insider told Daily Star Online: "The London auditions were a success and production want to keep things that way.
"Last year Amanda and Simon went rogue midway through filming in Manchester as they got hungry.
"It turned out they had snuck off to the kitchens to make beans on toast but thing didn't go to plan."
They continued: "Bosses smelt burning coming from the kitchen and went to investigate - they only just managed to stop the smoke alarms going off as they had burnt all the food.
"If production hadn't have acted and left Simon and Amanda to it the whole of the The Lowry Theatre would have had to be evacuated."