Lady Gaga has vowed to be a “warrior” for people fighting cancer after losing her best friend to the disease.

The US singer posted an emotional tribute to her friend Sonja Durham on Instagram, saying she was “in shock” and was now part of the family of people who have lost loved ones to cancer.

She shared a touching picture of the long-time friends clutching a balloon, saying: “I don’t know how to put a price on a friendship.

“I’m not even sure how you can assess the size of its meaning, only really your heart truly knows and it’s too special for words.

“I feel two competing feelings. Firstly, that I will live everyday with more passion, more determination, more compassion and more giving than ever before.

“Because that’s who she was, and it’s what drew us to each other, and I know it’s what she always wanted for me.

“She had this incredible way of releasing me from the anchor of my own sadness that held me back, she loved me fearlessly while I learned how to cope with fame and stay inspired no matter how scared I was.

“She knew all I cared about was the music. She made that ok.”

Gaga, 31, told her 24 million followers: “The other feeling I have is that of being robbed of the last 10 years of my life, friendship and career with her.

“Like someone took her from us, and with that taking took all the good times.

Lady Gaga.
Lady Gaga (Ian West/PA)

“I know that’s not true, and I know that I have those memories forever, I’m just in shock that I will never have new ones with her.

“I’m in shock that I won’t see her again until I pass too.

“I vow to be a little stronger everyday for her because that’s what she would have wanted, I vow to be stronger for anyone who’s lost somebody to cancer.

“I’m a part of that family now. I vow to be a warrior for her and be a voice for cancer patients so the world can continue to improve the dialogue and the fight. I loved her. I still love her.”

The singer said she has been busy preparing meals for her friend’s husband and stepson.

“I will keep cooking. Cooking my soul until it understands this,” she said.

Gaga said she told her friend to go and find her late Aunt Joanne, who she named her 2016 album after.

She said: “Last thing I told her, ‘Go find Joanne, Sonj’. Somehow I think she did.”

The star later shared a photograph of several dishes covered in foil, with messages of support for her friend’s husband written on them.

“For Sonja’s husband Andre,” she said. “Take care of those who you love who are suffering I think it helps us all to survive.”