The couple have been dating since 2006, although Diane – who is divorced from actor-and-director Guillaume Canet - has always insisted she has no intention of marrying again.
The pair attended a fundraising event in Monte Carlo yesterday. During the evening there was an auction, which is where Joshua snapped up the jewellery.
“Benefit officials said the Fringe star won a necklace by designer Carla Amorim with a bid of $45 000, reportedly overheard saying it was an engagement present for her,” a source told People.
Those close to the stars have insisted the speculation is untrue.
The Nights in Monaco event was staged at the Hotel de Paris, with stars taking time out from the Cannes Film Festival to attend.
Guests dined on veal, caviar and fish.
Over $750 000 was raised, which will go to Prince Albert of Monaco and former US President Bill Clinton’s foundations. The event was hosted by the royal, with Clinton giving a speech. The men announced their organisations will be teaming up in the future to work on worldwide issues such as the environment.
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