The 30-year-old Bulgarian has had his share of success on the tennis court too, having previously achieved a career high No 3 ranking.
He won Cincinnati back in 2017, his first and only Masters trophy, and followed up the win by taking the ATP Finals crown at the end of the season, his biggest title to date.
Meanwhile, Williams, a two-time former champion at the event herself, crashed out of the tournament early when it was held in New York as a one-off last year.
She lost her second match to Maria Sakkari from a set up, as the Greek overcame her 5-7 7-6(5) 6-1, but the woman often seen as the GOAT was able to storm back and make the semi-finals of the US Open a week later, defeating Sakkari en route.
