At what time of the install process a script is executed with 'preseed/run'?

[john doe <johndoe65534@mail.com>]

Debians,

From a preseed file I need to download and execute as the last command
a script.
I'm playing with 'd-i preseed/run string foo.sh' the script execute
successfully but does not look to be executed as the last command in the
install process.

Can someone confirm when 'preseed/run' is executed?

In other words, what is the best way to download and execute a script at
the end of the install process.

Any help is appreciated.

--
John Doe