It adds 1 to the last appeared block of numbers.

"(.*\D)(\d+)(\D+)?$"

\d = Number
\D = Non numeric character

This pattern will match to

Any characters + numbers with or without any character(s) that is/are not number at the end.
And you can refer back to each sub-matches that is inside the set of brackets afterwords.

For more details, google with the key words like "VBA" "Regular Expression" "Meta Character" etc.