Shannen Doherty has wished her ''beautiful friend'' Sarah Michelle Gellar a happy birthday.

The 'Buffy The Vampire Slayer' star celebrated her 40th birthday on Friday (14.04.17) and her good friend Shannen took to Instagram to share a sweet tribute to the blonde beauty.

Shannen - who was diagnosed with cancer in 2015 - praised Sarah for standing by her side throughout her battle with the illness, and thanked her for always ''rooting'' for her.

Posting a throwback photo of the pair at a party, the former 'Charmed' actress wrote: ''Happy Birthday @sarahmgellar I'm posting this pic because of the pure joy and fun, I am clearly having in your presence. From the moment we met, you embraced me, supported me and stood fiercely by my side. Never a moment of insecurity or feeling threatened between us. Instead, you only rooted for me and lifted me up. You are that woman that walks in a room and lights it up.... not only with your smile, but with your confidence, humility, intelligence and sense of ease. Naturally, you are an Aries!!! I love you. I'm proud of you. I also want you to come home now so we can celebrate!!! Happy birthday beautiful friend. You deserve the moon and more. (sic)''

The news comes after Sarah previously praised Shannen, 45, for the ''bravery'' she has displayed throughout her diagnoses, which she has openly documented on social media.

Sarah said: ''Shannen's incredible. What she's done for other women going through it is so brave, and that's what real bravery is - to be able to go through the hardest time of your life and show people it's OK to be scared, and it's OK to be vulnerable, and you can do it.''

And the 'Cruel Intentions' actress is amazed her close pal is still willing to take part in ''really hard'' dance classes with her, regardless of her debilitating condition.

Sarah - who has daughter Charlotte, seven, and four-year-old son Rocky with her husband Freddie Prinze Junior - said: ''The fact that she gets up and goes to those dance classes? The last thing I want to do is go to these really hard dance classes and sweat that hard and work that hard.

''I have to remind myself that if she's getting up there and doing it, then it's important that I do it, too.''