Go question

tester.go

package main

import (
	"fmt"
)

type type1 struct {
	number int
}

func (p *type1) String() string {
	return fmt.Sprintf("Type 1: %d", p.number)
}

type type2 struct {
	type1
	message string
}

func (p *type2) String() string {
	return fmt.Sprintf("Type 2: %s, %d", p.message, p.number)
}

type type3 type2

func main() {
	value := &type2{
		type1: type1{
			number: 1337,
		},
		message: "Hi there",
	}
	// Why does this print type1's String() rather than type2's?
	fmt.Printf("My value: %s\n", (*type3)(value))
}