Marko Djokovic (L) and Novak Djokovic of Serbia react during a doubles match against Mubarak Shannan Zayid of Qatar and Cem Ilkel of Turkey at the ATP Qatar Open tennis match in Doha, capital of Qatar, Dec. 31, 2018. Marko Djokovic and Novak Djokovic won 2-1. (Xinhua/Nikku)