Unable to combine the legend expression with the plain text together in Legend

  • What Grafana version and what operating system are you using?
    7.5.1 version and Win10

  • What are you trying to achieve?
    I want to put a plain text and legend expression together in Legend, for example, I have below metrics query:

And I use {{fs_device}} in Legend, it is presenting as below:
{device="/dev/mapper/rootvg-lv_root", instance=“”} Current: 97.5 GiB

But when I add “Total space” ahead of {{fs_device}}, it will no longer showing {device="/dev/mapper/rootvg-lv_root", instance=“”} any more, but only showing Total space.

What I want to achieve is to show something like below as Legend:
Total space: {device="/dev/mapper/rootvg-lv_root", instance=“”}

My variable: