Add the watermelon cubes and lime juice to a blender and liquify. Using a fine-mesh strainer, pour the watermelon and lime juice through the strainer into a large bowl. Press the remaining pulp through the strainer to squeeze as much liquid as possible into the bowl.

Stir the sweetened condensed milk into the watermelon lime juice until combined. Set aside.

In a large bowl add the heavy whipping cream. Using a hand mixer, whip the cream until stiff peaks form. Be careful not to overwhip the cream. When you pull up the beater, the cream should retain its stiff peak, that's when you know it's done.

With a spatula, gently fold the whipped cream into the watermelon mixture. Combine slowly to retain the whip in the cream but the mixture will be fairly liquid.

Transfer the mixture to an insulated ice cream tub or a metal tub and freeze for 4 to 6 hours. My preference is overnight.