Corollary
Tag 060M, permanent. Cite it as [Bourbaki, Tag 060M].
Algebra, chapter III, § 4. Tensor products of algebras
If Z and Z' are the respective centres of E and F, the centre of E \otimesK F is Z \otimes_K Z'*.
Let E and F be two subalgebras of an algebra G over a commutative field K; suppose that every element of E commutes with every element of F. Then the canonical injections define a canonical homomorphism (no. 2, Proposition 5) such that
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.