Kasi also shared the happy news on her own Instagram account, sharing a series of pictures of herself posing with her bump.
“Our golden child. Coming soon... Our greatest celebration... Our biggest blessing,” she wrote.
Shortly before announcing the baby news, Usain – who is an eight-time Olympic gold medallist – hinted that he and Kasi were ready to start a family together,
“Something I've learnt is it's never a good time to have kids,” he said. “It took me a while to figure that out. It's never a good time. You just have to buckle down and do it. It's in the near future, so, hopefully. We'll see.”
Chatting about his love-life last year, he told Daily Mail: “I’m not a single man but I just don’t put my love life out there that much.”
The couple have kept their relationship out of the media spotlight, and are not often pictured together in public. However Bolt confirmed their romance in 2016.
“We just got really serious, we are taking it one step at a time. I definitely want a family, though. For me, over the years, I've waited because I want to make sure it's the right person,” he told People at the time.
However, in 2016 the couple’s relationship appeared to be hanging by a thread after pictures emerged showing Usain kissing another woman in a Rio nightclub just hours before he spent the night with a 20-year-old student who shared WhatsApp images of them in bed.
The athletics star, who retired from running in 2017, is the only sprinter to win Olympic 100m and 200m titles at three consecutive Games.