Hefty surprise under the leaves!

I noticed this one tomato plant in my greenhouse was growing fruit faster than the others, as it was one of my ‘surprise seeds’ picked up at a roadside stall in the spring. I also wondered if it would get too heavy for the vine and the tomato supports that work well for my known plants . . Manitoba, Celebrity, Italia Roma, Juliet and Sweet Million. This hefty one weighing in at 1 pound 4 ⅝ ounces (or 583 grams) must have fallen quietly and peacefully in the night on to the soft earth. I wonder what it is? Almost too perfect to slice through it. I love garden surprises.