Unable to source zshrc during a terminal emulator's startup

Installed Tilix terminal emulator on Ubuntu 16.04 virtual machine and configured a json theme to my liking named theme.json.

I have added the same environment variables and aliases both in the .bashrc and the .zshrc as follows:

export VAR1=42
alias mydir=/path-to-my-dir/mydir

Created a launcher shortcut (tilix.desktop) which runs a script (tilix_launcher.sh) as follows:

# tilix.desktop
[Desktop Entry]
Encoding=UTF-8
Name=Tilix
Comment=Launch Tilix
Exec=/path-to-script/tilix_launcher.sh
Icon=com.gexperts.Tilix
Type=Application
# tilix_launcher.sh
tilix --session /path-to-json/theme.json

Confusingly, if on the 'normal' terminal source the zshrc and then open Tilix, the session has visibility of the zshrc; I do not understand how to automate that within a script (i.e. tilix_launcher.sh).

Versions:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.1 LTS
Release: 16.04
Codename: xenial
$ tilix --version
Versions Tilix version: 1.9.1 VTE version: 0.42 GTK Version: 3.18.9

The problem is that whenever I launch Tilix (with or without the launcher script), the environment variables and the aliases are not known to Tilix's session; have to source ~/.zshrc for them to work.

Tried to add this source command within the tilix_launcher.sh but it still does not work.

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