Serena Williams suffered with post-natal depression.

The 36-year-old professional tennis player has revealed she struggled with her mood after she gave birth to her daughter Olympia - whom she has with her husband Reddit co-founder Alexis Ohanian - last September following a difficult labour and once cried her eyes out because she couldn't find the little one's bottle.

Speaking to Britain's Harper's Bazaar, she said: ''Honestly, sometimes I think I still have to deal with it. I think people have to talk about it more because it's almost like the fourth trimester, it's part of the pregnancy.

''I remember one day, I couldn't find Olympia's bottle and I got so upset I started crying ... because I wanted to be perfect for her.''

Serena recently admitted that she almost died delivering Olympia as she had to undergo an emergency caesarean section but experienced life-threatening complications, which resulted in surgery to prevent blood clots travelling to her lungs.

She said recently: ''One minute, everything's going according to plan, and then I'm being wheeled off for surgery. I was terrified, and it was a whole new kind of fear.''

Her husband, Alexis, added: ''The C-section was low on our wish list because of her history with blood clots. Any surgery that Serena has is potentially life-threatening. But we decided, 'Well, OK, for the safety of mom, for the safety of the baby, we have to proceed with a C-section.''

And the frightening experience has just pushed her to become the best of the best.

She explained: ''For so many years, I defined myself in just one way: by success, by championships, by making history. And then, all of the sudden, my life changed forever. It wasn't part of any plan to have this happen, not while I was still on top. But two years ago, I met this man, almost out of nowhere. We fell in love, and then, this unthinkable surprise. I can't believe how much went wrong on my way to meeting her. I almost died. But now, she's the reason why this all means even more than it did before. Still, there's no escaping the fear. The fear that I might not come back as strong as I was. The fear that I can't be both the best mother and the best tennis player in the world. I guess my only choice is to live and find out.''