Andy Murray is back competing on the grand slam tour, and will launch his US Open campaign on Monday August 30.

The tennis ace is often pretty active on social media during his tournaments, so you might have noticed that he uses the hashtag #AMC to sign off his posts.

Here's what AMC stands for and why Andy Murray uses it...

What does AMC mean? 

Andy Murray has been signing off his Twitter and Instagram posts using #AMC for some time, which has left some followers wondering what it stands for. 

AMC stands for Andy Murray x Castore, the  British sportswear brand which partners Murray and has done so since January 2019. 

Aside from the professional partnership, Murray is also a shareholder in the company.

Murray will be fully kitted out in Castore sportswear throughout the US Open championships, as he was for Wimbledon earlier this summer. 

In fact, the three-time grand slam champion has helped design his matchwear. 

He said: "I work with the AMC designers on every piece, with technical performance at the heart of the process. 

"It's important that the kit performs under the toughest conditions. 

"I really enjoy testing it, giving it my feedback and being part of the design process."

The AMC designs aim to combine "the respective brand ethos of Andy Murray and Castore, created to deliver a new standard in tennis performance clothing on and off the court," according to the brand's website. 

People can shop the range online, including Murray's own on-court look. 

Who else do Castore partner?

Andy Murray isn't the only famous sportstar that Castore partners. 

In fact, it racks up a huge number of top performing athletes including Adam Peaty, who defended his Olympic title earlier this summer. 

Castore also works with F1 experts McLaren and football teams Rangers and Newcastle United.