Both former Olympic swimmers, they teamed up last year in the royal's native South Africa for the Midmar Mile, an open water swimming challenge.
After the race across a lake, wearing bathing suits and goggles, the pair were pictured exchanging high fives.
CLICK ON PHOTOS FOR FULL GALLERY
This week's black tie meeting was in Germany when the princess and husband Prince Albert were hosted by the country's President Joachim Gauck and his partner Daniela Schadt.
The couple looked thrilled to catch up with german swimming chap Franziska, who was also a guest when they married in a beautiful open air ceremony in the courtyard of the Prince's Palace in Monte Carlo.