Dearest Theresa,

On this journey as a swimmer, there are three things that I am most grateful for. Number one would be for the achievements I have had in and out of the pool. Number two is for the social impact I have been fortunate enough to create. And number three is for the people I have met along the way.

Especially you.

Our friendship was not one that was immediate. In fact, we only became friends almost a year and a half after I was in the team. We were roommates in Brazil in September 2005 and for every trip thereafter we have been roommates.

I remember once, when I was in class in 2010, I decided to check the rankings. I saw my competitors were getting faster than me and I was stricken with panic. However you calmly told me not to worry about it and to instead focus on myself. I will carry this advice and use it for the rest of my life.

For 15 years we have been training alongside each other, including for the Paralympics in Beijing 2008, London 2012 and Rio 2016. Thank you for the motivation, encouragement and company.

I could not have had a better teammate to push me on as we trained for Rio. When you received your bronze medal, I was ecstatic. I was so, so, so happy for you. I have always believed that the amount of hard work put in will show and it did show with your amazing times.

The journey has not been an easy one. We were always tired. It was literally blood, sweat and tears. The blood taken for physiology testing, sweat at training and the amount of tears cried into our goggles when it was an especially rough day.

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At times we were angry at each other over the smallest things as emotions ran high during stressful periods. But we could never stay mad at each other because we understood each other's journeys. We were both trying to reach common goals and thank you for being there at every moment.

You went back on Tuesday after your races at the world championships and it felt weird not to have you around. When I became world champion again on Wednesday, I wanted to text you to come down for dinner when I got back to the hotel. Then I remembered that you were not in London any more and so I called you on FaceTime instead.

I have always been able to depend on you as a friend, for advice or just when I needed a listening ear. I have been very fortunate to have you go through all this with me.

Come October when I get back into the water and start training hard for Tokyo 2020, I have no idea how things might change. But I do know that even though you will not be in the pool alongside me any more, I can still depend on you to be there for me in life.

Pin Xiu