Linebreak spacing for saved string

Question

I have a string called \subtitle, and that string comes up at multiple locations. This string contains a linebreak, so that it shows up better at the front page. I define this string in main.tex

\subtitle{Teaching Robots Dynamic Interaction Tasks\\
by Performing Demonstrations}

Now I also have a title page, in which this string also shows up. But the vertical spacing between the lines is a bit messed up. If I print the string with

{\makeatletter
\ifdefvoid{\@subtitle}{}{\titlestyle\fontsize{30}{80}\selectfont\@subtitle}
\makeatother}

with an extravagant spacing between lines, it shows up like this:

Since the string does not fit at one line, it automatically breaks the string between the words 'Dynamic' and 'Interaction', which is totally fine, and it puts the vertical space of 80 between those lines. The desired result is that this vertical space also shows up between the second and third lines also at 80. How do I do this? I don't want to alter the string \subtitle, since I also use this string at the frontpage.

Answer 1

Insert the string \subtile into a parbox to make the title page.

\documentclass[12pt,a4paper]{article}

\title{Main Title}

\newcommand{\subtitle}{Teaching Robots Dynamic Interaction Tasks\\
    by Performing Demonstrations}

\begin{document}    
    
    \parbox{\textwidth}{\centering \fontsize{30}{80}\selectfont \subtitle}
    
\end{document}