Yes, just not humanoid
Ask Pope or your religious authority.
Remote control animal is a fact. We can do it. We did it.
In 2013, researchers reported the development of a radio-telemetry system to remotely control free-roaming rats with a range of 200 m. The backpack worn by the rat includes the mainboard and an FM transmitter-receiver, which can generate biphasic microcurrent pulses. All components in the system are commercially available and are fabricated from surface mount devices to reduce the size (25 x 15 x 2 mm) and weight (10 g with battery)
Sadly, we pretty much did it to other humans. See Lobotomy. I sure hope your scientists will find a way to just grow brain without some parts instead of destroying parts after, but sure, such a brain can exist.
The size has to be at least 50 meters
The holotype (and now lost) vertebra of Amphicoelias fragillimus may have come from an animal 58 metres (190 ft) long;
So yes, this size is achievable for animal, if only barely. For why not humanoid, see:
Most of the problems is about muscle cross-section area VS weight, and metallic parts only makes that harder. And if you are going for mechanical skeleton and muscles, mechanical heart, electronic steering, what else is left to make it "biological"? It would be more mechanical mech with some bio parts... But what would be the use for bio parts in such a thing?
If alien DNA would solve muscle strength issue, and you'll use composite bones / exoskeleton (or, you know, alien ones), it may work for humanoid, why not.