Lady Gaga marks Tony Bennett's 89th birthday with 'towering' cake

Lady Gaga surprised singer Tony Bennett with a special serenade and a massive cake to honor him on his 89th birthday.

In the final moments of the pair's last show at the Kennedy Center, the 29-year old singer sang the Duke Ellington's "I'm Beginning To See The Light" to a beaming Bennett, and then led the crowd in singing "Happy Birthday", the People Magazine reported.

According to the sources, the cake, created by Duff Goldman's Charm City Cakes, of Food Network fame, towered over both Gaga and Bennett.

The 'Poker Face' singer took to Instagram to share the details of the sweet confections and wrote "missasiakinney and Happy made it too!"

The singer also shared a video of the birthday performance to her millions of Twitter followers.

The concert of Grammy-winning album 'Cheek to Cheek' marked the end of the duo's lengthy seven-month tour, for which Gaga and the 'Body and Soul' singer had gone to Spain, Italy, Denmark and Monaco, among other places.