Modeling vs losing bet: World no.1 Djokovic takes up 10-yr challenge

World number one men's tennis player Novak Djokovic shared two pictures of himself in just underwear as part of the viral 10 year challenge. "#10YearChallenge modeling vs losing a bet to your brother," the 31-year-old Serbian tweeted. Reacting to Djokovic's post, users tweeted, "Please ask your brother to bet with you often!" and "Some things never change".