If you replace every part of a ship, is it still the same ship?

Theseus has a ship. Over time, every plank rots and gets replaced, one by one, until none of the original wood is left.

So is it still his ship?

Same name, same shape, same crew, and it never stopped sailing. But literally not a single original piece remains.

If someone collects all the old planks and rebuilds a ship out of those, now there are two. Which one is the real Ship of Theseus?