Multlined in align environment: letter before alignment point

I have two equations, one of which is very long. I would like to have a single alignment, at the = sign. At the same time, I would like to split the long equation into multiple lines. I have tried to use multlined, but I am not able to obtain the desired result.

Here is a minimal working example:

documentclass[12pt]{amsart}
usepackage{mathtools}

begin{document}

begin{align*}
F &= a + b
G &= begin{multlined}[b](c + d
    {} + e + f + g + h)
    end{multlined}
end{align*}

end{document}

It typesets as shown below:

I am aware of this question, yet the presence of G before the alignment point makes its solution not directly applicable to my case.

documentclass[12pt]{amsart}
usepackage{mathtools}

begin{document}

begin{align*}
    F &= a + b
    G &= begin{multlined}[t]
            (c + d              
            {} + e + f + g + h)
        end{multlined} 
    H &= i + j + k
end{align*}

end{document}