The race of his life! Michael Phelps reveals how he took on a great white shark

Michael Phelps is swimming for his life against a great white shark in what may be one of the most talked about races of his career.

Phelps vs. Shark: Great Gold vs. Great White for Shark Week kicks off July 23 on Discovery.

The opening night special which was filmed last month, tests the 23 time Olympic gold medalist, Phelps, against a variety of sharks.

Technically such a race would be difficult, but Phelps explained just how these 'races' were done. 'We were off the tip of Cape Town in South Africa and set up, almost, a lane where I was able to swim in a straight line. We were in open water, but we did not have a shark literally next to me swimming,' he says.

When it was time for the sharks to take one of the world's fastest swimmers it was calibrated a bit differently.

'The challenge of trying to get a white to swim in a straight line was difficult, because when a white attacks a seal on the surface they come from under the surface to build speed to be able to get that natural breach that we all see from great whites,' Phelps told Yahoo! TV.

'But I think with some of the tests that we were running out there on the boat, we were able to see what they can do.'

When it was time for the sharks to take one of the world's fastest swimmers it was calibrated a bit differently.

'The challenge of trying to get a white to swim in a straight line was difficult, because when a white attacks a seal on the surface they come from under the surface to build speed to be able to get that natural breach that we all see from great whites,' Phelps told Yahoo! TV.

'But I think with some of the tests that we were running out there on the boat, we were able to see what they can do.'

helps dove with a whale shark in the Maldives after the 2012 Olympics and had diving with great whites on his bucket list explains he wasn't nervous to get in the water in Cape Town because of the sharks.

'We had an abundance of divers underneath of me and camera guys all over the place, so I felt very safe and comfortable,' he says.

Yet, he was still nervous.

'As you see me getting ready for the race in Cape Town, you see focus on my face, and I think that was partially because I was trying to mentally prepare myself for the temperature of the water,' he says.

'The water was very cold. I knew it was going to be cold, but swimming in 55 degree water when normally it's about 80 when I swim in it, that's a significant difference.'

'I would say probably the worst part about it was the cold water.'

What stroke will he swim? Freestyle or his signature, butterfly?

Phelps wont give up on the stroke technique he used in his shark challenge. 'We'll leave that one a secret,' Phelps says. 'I wasn't fully expecting the temperature of the water, so you guys are going to have to tune in to watch.'

Phelps and family may just gather around to watch together as he and his wife Nicole Johnson threw his son Boomer an adorable one-year-old shark themed birthday party.

Seems like little Boomer is a fish to water in the family, getting into the spirit just in time for Shark Week, and dad's debut that will begin and close out the week.

Shark Week closes July 30 with a second special featuring the GOAT, Shark School With Michael Phelps.

Doc Gruber and Tristan Guttridge of the Bimini Shark Lab give him a crash course that Discovery says will dispel misconceptions, get him up close to the power of a great white, and teach him how to safely dive with sharks — including how to stay calm when a hammerhead swims two feet above his face.

So what is the trick for that? Phelps laughs again. 'I think it was about six inches from my face. It was really close to me,' he says.

'I guess it's probably doing more common sense stuff than you think about. It's not freaking out, trying not to flail your arms all over the place. Not splashing into the water and making a gigantic wave, because that's obviously going to attract them to come up and see what's jumping in their environment and try and check it out. … We look at these animals as dangerous animals but they're not; they're out there trying to survive just like we are on land.'