This one regex check will validate if the string is formatted to be an IP address, but it won’t actually validate the octets.  It’s still useful.

If (($IPAddress -match "\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}") -and ($IPAddress [$IPAddress .Length -1] -match "\d")) {"This is formatted like an IP Address."}