London, Aug 9 - Hollywood actor Mel Gibson's Russian girlfriend Oksana Grigorieva has not only convinced him to get fitter but has talked him into taking a new exercise regime.

Gibson, 53, has embarked on a tough new diet-and-fitness regime. Grigorieva, who is 14 years younger and is pregnant with their first child, due this autumn, is keen that he eats more healthily.

Gibson was reportedly overheard telling a pal: 'It's all very tiring. I hope it's all worth it in the end.'

The actor's wife of 28 years Robyn filed for divorce last April citing 'irreconcilable differences'. The couple, who have seven children together, released a joint statement saying: 'Throughout our marriage and separation we have always strived to maintain the privacy and integrity of our family and will continue to do so.'