The turquoise and black bracelet was made with loom bands, the jewellery obsession which is sweeping Britain's primary schools.
CLICK ON PHOTO FOR GALLERYDuchess of Cambridge née Kate Middleton, was also seen wearing a similar bracelet during the Royal Tour of Australia and New Zealand in April. Kate's was a gift from two young girls.
It was unknown who made the bracelet for William, but it is thought to be a gift from a well-wisher at Wednesday's event.
The Prince also received what is thought to be the first birthday present for his son, Prince George's. The brown paper bag had a gift tag which read: "Happy birthday Prince George. With lots of love from all at Earlsdon Primary School, Coventry".
The Duke was in Coventry to visit the Cambridge War Memorial Park where he attended a reception and gave a short speech. He also laid a wreath on the monument and paid his respects to fallen soldiers.
Prince William described Britain's green spaces as "a vital part of our national heritage".
He added: "Each moment of play or use that takes place on a memorial field is, in a way, an act of remembrance."
The Prince also urged people not to take green spaces for granted and praised Coventry City Council's leading example, and said: "I have no doubt that they will succeed, but only if they have help."
He later walked through the park and watched a local primary school's sports day. He also took part in a tennis match.
As President of the Fields in Trust (FiT) charity, the park is the first to be dedicated as part of the Centenary Fields programme in partnership with the Royal British Legion.