Local projectivity of Lagrangian fibrations on Hyperk\"ahler manifolds

We show that if $f:X\to B$ is a Lagrangian fibration from a compact connected K"ahler hyperk"ahler manifold $X$ onto a projective normal variety $B$, then $f$ is locally projective. This answers a question raised by L. Kamenova and strengthens a former result (\cite{Ca05}, Proposition 2.1), according to which the smooth fibres of $f$ are projective. The proof below does not use the known additional results concerning fibres and base in this specific context).