Article continues below advertisementOK! can reveal George Clooney and his wife, Amal, are facing an unexpected challenge with their picturesque $16 million riverside mansion in Sonning - a slump in local property values that has knocked millions off its worth.The Hollywood power couple, both now 64 and 47 respectively, purchased their Grade II-listed home on the Berkshire-Oxfordshire border in the U.K. in 2014, describing it at the time as their dream retreat from the glare of Los Angeles.