Store hex value as string (Arduino project)

I'm working on an Arduino project and I want to store a hex value as string.

eg: Hex is C697C63B

for (byte i = 0; i < bufferSize; i++) {
     Serial.print(buffer[i], HEX);
}

I would like to store the String as x = "C697C63B";

  String CardID = "";
  for (byte i = 0; i < bufferSize; i++) {
    CardID += (buffer[i],HEX);
    Serial.println(CardID);
  }

But the Sting is stored as CardID = 16161616

Sorry I just start C++ for a week and I spend 3 day already just to find answer.

Okay i found the answer now thank you everyone that help

  String CardID = "";
  for (byte i = 0; i < bufferSize; i++)
    CardID += String(buffer[i], HEX);
  Serial.print(CardID);