One multiline equation and many single line equations inside align environment [duplicate]

Question

Here is a MWE.

\begin{align}
  \label{eq:4}
  \begin{aligned}
    r'_0(s)
      & =\gamma \Omega_{i} \exp(\gamma s \Omega_{i}) r_0(0)
      \exp( -\mu s \Omega_{i} \\
      & \qquad - \mu \exp(\gamma s \Omega_i) r_0(0)
      \exp(-\mu s \Omega_{i}) \Omega_{i} \\
      & = \gamma \Omega_{i} r_0(s) - \mu r_0(s) \Omega_{i} \\
      \end{aligned} \\
  {add another multiline equation like the first two lines here}
\end{align}

But the output is not ideal because the equation number in the second line is below the actual equation. It is probably expecting another multiline equation. I would like to keep the equation number on the same line as the second equation. How can I fix this?

Edit: I intend to add a third line which once again will have a multiline equation. So I must use the aligned environment. Therefore simply turning off the equation numbers won't solve this problem. Therefore I do not think it is not a duplicate of This question. Actually, I got inspiration from the answer to this answer. This question has a parallel with that question if any.

Here is the output from the above piece of code

Answer 1

I would do it using \nonumber command inside a single align:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \begin{align}
    r'_0(s)
      & =\gamma \Omega_{i} \exp(\gamma s \Omega_{i}) r_0(0)
      \exp( -\mu s \Omega_{i} \nonumber\\
      & \qquad - \mu \exp(\gamma s \Omega_i) r_0(0)
      \exp(-\mu s \Omega_{i}) \Omega_{i} \label{first}\\
      & = \gamma \Omega_{i} r_0(s) - \mu r_0(s) \Omega_{i} \label{second}
  \end{align}

  the equation \eqref{first} is above the equation \eqref{second}.
\end{document}

I think you can expand this way in your needs.

Output:

EDIT: After OP's edit and after accepting:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \begin{align}
    &\begin{aligned}\label{first}
    r'_0(s)
      & =\gamma \Omega_{i} \exp(\gamma s \Omega_{i}) r_0(0)
      \exp( -\mu s \Omega_{i} \\
      & \qquad - \mu \exp(\gamma s \Omega_i) r_0(0)
      \exp(-\mu s \Omega_{i}) \Omega_{i} 
     \end{aligned}\\
    &\begin{aligned}\label{second}
      \phantom{ r'_0(s)}& = \gamma \Omega_{i} r_0(s) - \mu r_0(s) \Omega_{i}
      \end{aligned}
  \end{align}

  the equation \eqref{first} is above the equation \eqref{second}.
\end{document}

This is a way used aligned environment with the next output:

As you can see the numbers are vertically centered. Also I have not reason to use the aligned but adding for OP's "unknown specific needs" :P