Usain Bolt has got engaged.

The legendary sprinter turned 40 on August 21, and during his birthday celebrations, he popped the question to longterm partner Kasi Bennett - the mother of his children Olympia Lightning, six, and five-year-old twins Thunder and Saint Leo.

Photos shared by the Jamaica Observer on Instagram featured the eight-time Olympic gold medalist, who was wearing a beige checked suit, getting down on one knee while holding a microphone in front of the model.

Another picture showed them embracing after he proposed in front of family and friends at the event.

There was also a shot of Kasi's new five-carat engagement ring, which featured a pear shaped diamond in between several other diamonds.

Ahead of the celebrations, Kasi had taken to Instagram to pay tribute to her partner, who she has been in a relationship with since 2013

She wrote: "Happy 40th birthday to my person. My love, my home, my forever. You are an incredible dad and truly the centre of our little world."Your legacy is extraordinary, but the man behind it will always be what makes me proudest. So grateful to do this fun life we've created with you. I love you endlessly baby."

Usain previously revealed he and Kasi had agreed not to have any more children after their twins were born.

Speaking when the boys were three months old, he told The Times newspaper when asked if they would plan more kids: "No, we both agree that that's it."

Usain also confessed he wasn't keen to be at the birth of his children but Kasi urged him to support her.

He admitted: "I didn't want to be there, but Kasi was, like, 'Oh, please!' My dad told me, 'Whatever happens, do not look.'

"[Did I look?] No!"

The sportsman credits parenthood for helping him to calm down and take life more slowly.

He said: "[Parenthood] has made me much more patient. People always ask me why I couldn't coach [athletics]. I was, like, 'I'm not the patient type of guy.' [Becoming a father has] really calmed me down and let me know how to live at a slower pace."

Usain hopes at least one of his children follows in his footsteps and forges a career in athletics.

He said: "Yeah, definitely. I don't care who."