Let $(M,J,g,\Omega)$ be a compact Calabi–Yau $m$-fold and $\{L^{t}:t\in[0,T)\}$ a family of compact, immersed, graded Lagrangians in $M$ satisfying Lagrangian MCF, with a finite time singularity at $t=T$. Then at some singular point $x\in M$ of the flow there exists a type II blow up.

That is, identifying $M$ near $x$ with $T_{x}M\cong{\mathbin{\mathbb{C}}}^{m}$ near $0,$ there exist sequences $(t_{i})_{i=1}^{\infty}$ in $[0,T),$ $(x_{i})_{i=1}^{\infty}$ in $M$ and $(\lambda_{i})_{i=1}^{\infty}$ in $(0,\infty),$ such that $t_{i}\rightarrow T,$ $x_{i}\rightarrow x,$ $\lambda_{i}\rightarrow\infty$ and $\lambda_{i}^{2}(T-t_{i})\rightarrow 0$ as $i\rightarrow\infty,$ and for each $s\in{\mathbin{\mathbb{R}}}$ the limit

exists as a nonempty, noncompact, smooth, closed, immersed, exact, graded Lagrangian in ${\mathbin{\mathbb{C}}}^{m}$ whose mean curvature $\tilde{A}^{s}$ is nonzero (so that $\tilde{L}^{s}$ is not a union of Lagrangian planes in ${\mathbin{\mathbb{C}}}^{m}$). All derivatives of $\tilde{A}^{s},$ and the phase function $\theta_{\smash{\tilde{L}^{s}}},$ are uniformly bounded independently of $s\in{\mathbin{\mathbb{R}}}$. Also $\tilde{L}^{s}$ depends smoothly on $s\in{\mathbin{\mathbb{R}}},$ and $\{\tilde{L}^{s}:s\in{\mathbin{\mathbb{R}}}\}$ satisfies Lagrangian MCF in ${\mathbin{\mathbb{C}}}^{m}$.