The reformed party animal had already reportedly given up alcohol out of sympathy for pregnant Meghan, but now he's drinking mineral water instead of caffeine, the Sunday Express reports.
The Duke of Sussex's new health kick meant he looked fitter and bright-eyed at Sandringham for Christmas - and it hasn't gone unnoticed by the royal family.
A source told the Express: 'Considering he's been a pretty brutal drinker since he was a young teenager, it's quite an achievement.'
The Duchess of Sussex, 37, has also introduced Harry to yoga and has encouraged him to exercise more, showing him an alternative way to live claims the source.
The new exercise regime and lack of booze has meant that friends think the 34 year old is 'more chilled and relaxed'.
A source said: 'All she did was show him there's another way to live and he's become a huge fan.
'He eats well, doesn't poison his body, exercises, does a bit of yoga and is a lot happier.'