Using multiple interfaces in Golang

I'm learning Golang and as an exercise in using interfaces I'm building a toy program. I'm having some problem trying to use a type that "should implement" two interfaces - one way to solve that in C++ and Java would be to use inheritance(there are other techniques, but I think that is the most common). As I lack that mechanism in Golang, I'm not sure how to proceed about it. Below is the code:

var (
    faces = []string{"Ace", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"}

    suits = []string{"Hearts", "Diamonds", "Spades", "Clubs"}
)

type Card interface {
    GetFace() string
    GetSuit() string
}

type card struct {
    cardNum int
    face    string
    suit    string
}

func NewCard(num int) Card {
    newCard := card{
        cardNum: num,
        face:    faces[num%len(faces)],
        suit:    suits[num/len(faces)],
    }

    return &newCard
}

func (c *card) GetFace() string {
    return c.face
}

func (c *card) GetSuit() string {
    return c.suit
}

func (c *card) String() string {
    return fmt.Sprintf("%s%s ", c.GetFace(), c.GetSuit())
}

What I'm trying to achieve:

• I would like to hide my struct type and only export the interface so that the clients of the code use only the "Card" interface
• I would like to have a string representation of the struct, hence the implementation of the interface with the "String()" method in order to be able to call "fmt.Println()" on instantiations of my struct

The problem comes when I'm trying to use a new card though the "Card" interface and also trying to get the string representation. I cannot pass the interface as the parameter of the implementation of the "String()" method as there is a compiler error which is related to the addressability of an interface at the core language level(still digging through that documentation). The very simple example of testing exposes the issue:

func TestString(t *testing.T) {
    card := NewCard(0)
    assert.EqualValues(t, "AceHearts ", card.String(), " newly created card's string repr should be 'AceHearts '")
}

The compiler tells me, for good reason, that "card.String undefined (type card has no field or method string)". I could just add the "String()" method to my "Card" interface, but I do not find that to be clean: I have other entities implemented with the same model and I would have to add that redundancy everywhere; there is already an interface with that method.

What would be a good solution for the above issue that I'm having?