Removing 3 specific characters, if present from the start of a string VB.net

Question

I have a situation where I need remove a prefix from a string, if it exists.

Dim str As String = "samVariable"

Needs to be converted to Variable

Easy, with TrimStart

str = str.trimstart("s"c, "a"c, "m"c)

Except...

The string might not always start with "sam"

Example:

Dim str As String = "saleDetails"

This will now become aleDetails

Which is wrong, so how about Replace

str = str.Replace('sam','')

Brilliant! Now:

Example 1:

Dim str As String = "samVariable"
str = str.Replace('sam','')
str = "Variable"

Example 2:

Dim str As String = "saleDetails"
str = str.Replace('sam','')
str = "saleDetails" (unaffected)

BUT....

What if:

Dim str As String = "Resample"
str = str.Replace('sam','')
str = "Reple"

This is wrong again!

So, my question is:

How do I remove "sam" from the beginning of a string only?

I had expected TrimStart("sam") to work, but it doesn't

Answer 1

str = New Regex("^sam").Replace(str, String.Empty)

The regular expression looks for sam at the start of the string and replaces it with empty, effectively removing the sam from the beginning.

EDIT Per Konrad's comment, the shared method call would be better:

str = Regex.Replace(str, "^sam", String.Empty)