Writing in an article for Vogue magazine, the 23-time grand slam champion said she wants to spend more time with her family and have more children with husband Alexis Ohanian.
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The 40-year-old said the US Open will be her final tournament before she hangs up the racquet for good.
"I have never liked the word retirement," she wrote.
"Maybe the best word to describe what I'm up to is evolution. I'm here to tell you that I'm evolving away from tennis, toward other things that are important to me.
"A few years ago I quietly started Serena Ventures, a venture capital firm. Soon after that, I started a family. I want to grow that family."
The American champion made mention of Barty and Wozniacki - two former World No.1s who retired at the top of their game.
However she said her own retirement is vastly different and she doesn't feel any sense of enjoyment or relief in making the decision.
“I know that a lot of people are excited about and look forward to retiring, and I really wish I felt that way,” she admitted.
“Ashleigh Barty was No.1 in the world when she left the sport this March, and I believe she really felt ready to move on.
"Caroline Wozniacki, who is one of my best friends, felt a sense of relief when she retired in 2020.
“Praise to these people, but I’m going to be honest. There is no happiness in this topic for me. I know it’s not the usual thing to say, but I feel a great deal of pain.
"It’s the hardest thing that I could ever imagine. I hate it. I hate that I have to be at this crossroads. I keep saying to myself, I wish it could be easy for me, but it’s not.”
Serena Williams' pointed dig at Margaret Court
Williams also managed to take a parting shot at Aussie tennis great Margaret Court, referencing the fact she's been stranded on 23 grand slam titles - one behind Court's all-time record - for over five years.
Williams made sure to mention the fact that Court won all of her majors before the professional era of tennis began, a point of contention when fans are discussing the 'GOAT' debate.
"There are people who say I'm not the GOAT (greatest of all time) because I didn't pass Court's record, which she achieved before the 'Open era' that began in 1968," the former World No.1 said.
"I'd be lying if I said I didn't want that record. Obviously I do. But day to day, I'm really not thinking about her.
"If I'm in a Slam final, then yes, I'm thinking about that record. Maybe I thought about it too much, and that didn't help."
Williams won her 23rd major at the Australian Open in 2017 while pregnant with daughter Alexis Olympia, and appeared destined to equal and pass Court's record of 24.
But she has lost four grand slam finals since that time and has never managed to make it to the elusive 24.
“The way I see it, I should have had 30-plus grand slams," she said.
"I had my chances after coming back from giving birth. I went from a C-section to a second pulmonary embolism to a grand slam final. I played while breastfeeding. I played through post-partum depression.
“But I didn’t get there. Shoulda, woulda, coulda. I didn’t show up the way I should have or could have.
"But I showed up 23 times, and that’s fine. Actually it’s extraordinary. But these days, if I have to choose between building my tennis resumé and building my family, I choose the latter.”
The 40-year-old played down expectations about her swansong at the US Open after losing in the first round at Wimbledon in June after a year-long absence from the tour.
"Unfortunately I wasn't ready to win Wimbledon this year. And I don't know if I will be ready to win New York. But I'm going to try," she wrote.
"I know there's a fan fantasy that I might have tied Margaret that day in London, then maybe beat her record in New York... It's a good fantasy. But I'm not looking for some ceremonial, final on-court moment.
"I'm terrible at goodbyes, the world's worst. But please know that I am more grateful for you than I can ever express in words... And I'm going to miss you."
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