Here's the major clue that led to the rumors: Vogue Editor-in-Chief Anna Wintour's name was on the guest list made up of mostly family members, and it's unlikely that she'd go and not feature the wedding in her magazine.
Additionally, both Anna and George raised millions during the Obama re-election campaign in 2012 and Anna's friend Oscar de la Renta is designing the gown for George's bride Amal Alamuddin. Giorgio Armani was picked to outfit George's tuxedo.
Earlier this week we learned that George and Amal had taken out a marriage license in London -- the first legal steps required before the two tie the knot.
The couple met in September 2013 and got engaged in April. They are reportedly planning for a wedding in Italy some time next month.