How to right align QED at a specific line within align environment? [MWE]

I have a proof which is concluded by a long, multi-line equation. I would like to place the QED right-aligned on the same line as the last line of the equation.

Without qedhere, I get the desired right-aligned QED, except it’s on a new line with undesired vertical space. I tried using hfill but it didn’t appear to do anything.

Here’s a MWE.

documentclass{report}
usepackage{amssymb,amsthm,amsmath}

newtheorem {lemma}{Lemma}
begin{document}

begin{lemma}
This is a lemma.
end{lemma}
begin{proof}
Proof includes a long, multi-line equation.
begin{align*}
a &= b 
  &= c 
  &= d. qedhere
end{align*}
end{proof}

end{document}

How do I right align the QED on the same line as the last line of the equation? Thanks in advance for any insight.

usepackage{amssymb,amsmath,amsthm}