Heat oven to 350 degrees F. Spray a bundt pan with non stick cooking spray.
Combine cake mix, instant pudding mix, eggs, water and vegetable oil in a large bowl. Mix with a hand mixer until smooth, approximately 2 minutes, scraping the batter down to ensure everything gets well blended.
Take out 1 cup of the batter and place in a small bowl. Add ½ cup chocolate syrup to the bowl and mix together.
Pour the cake mix batter into the bundt pan and then pour the chocolate syrup mixture on top. Use a knife to swirl the two colours of batter together. Don’t mix too much as you want to be able to see the swirls.
Bake for approximately 55 minutes until a toothpick inserted into the batter comes out clean.