Multlined in align enviromnent: alignment of = and equation numbering

Question

I'm using the multlined environment inside an align environment and want have the = aligned at the top and the equation numbering at the bottom. Is this possible?

Here my MWE:

\documentclass{article}
\usepackage{mathtools,amsmath}
\begin{document}
\begin{align}
y &= a+b+c \\
&= \begin{multlined}[t]
a+b+ \\
c
\end{multlined}
\end{align}
\begin{align}
y &= a+b+c \\
&= \begin{multlined}[b]
a+b+ \\
c
\end{multlined}
\end{align}
\end{document}

Answer 1

You have to place the = inside multlined; in order to get alignment, though, a \! is necessary (multlined does the same as aligned and gathered that add \, at their left border).

\documentclass{article}
\usepackage{amsmath,mathtools}

\begin{document}

\begin{align}
y &= a+b+c \\
  &  \!\begin{multlined}[b]
     = a+b+{} \\
          c
     \end{multlined}
\end{align}

\end{document}