Michelle Obama tweets birthday love to 'grayer' Barack

Michelle Obama took to Twitter today to send her husband an affectionate birthday message -- and a gentle ribbing about the US President's graying hair.

"Happy birthday, Barack! Your hair's a little grayer, but I love you more than ever," Michelle Obama wrote on her official twitter account, @FLOTUS.

The message was accompanied by an undated black and white photo of the Obamas as a young couple relaxing on a sofa.

Barack Obama is spending his 52nd birthday weekend at Camp David, the rural Maryland retreat made available to US Presidents. He was to return to Washington later today.