Celerities are backing a new social media craze to try to help an eight-year-old girl who is in desperate need of a bone marrow donor.
Wales rugby union captain Sam Warburton and comedian Russell Howard are among the stars who have posted a picture of themselves online wearing pants on their heads in a bid to encourage people to sign up to the register in order to find a matching donor for Hollie Clark.
Hundreds of pictures with the caption #HelpHollie have appeared on Facebook and Twitter as members of the public followed suit.
Hollie, from Cardiff, has a rare bone marrow syndrome called myelodysplastic syndrome (MDS) and is in desperate need of a bone marrow donor, a s pokeswoman for charity Anthony Nolan said.
Her parents, Laura and Stephen, launched the campaign to encourage people to sign up to the charity's register. The youngster and her family have also posed for pictures with their underwear on their heads.
As a result of the #pantsonyourhead campaign there has been a 2,580% increase in the number of people in Wales signing up to its bone marrow register in just over two weeks compared with the same period last year, the charity said.
Hollie was diagnosed with MDS, a disorder which causes a fall in the number of healthy blood cells in the body, in April after developing unusual bruising.
She is surviving on blood transfusions until a suitable donor can be found through the Anthony Nolan register.
Her mother, a GP, said: " It was an absolute shock, it is literally the worst thing as a parent you could be told.
" It was hard to believe because she'd been so active at the time - she loves swimming and cycling and playing with her friends, and she'd been doing all these things without us even knowing that her haemoglobin levels were dangerously low."
On the creation of the campaign, Mrs Clark added: "Hollie was feeling really unwell after her first round of blood transfusions, and at this time the only way some of our family could communicate with her was by using FaceTime.
"Her uncle, Matthew, put his underwear on his head to make her laugh while he was talking to her on FaceTime and it sparked an idea for a way we could raise awareness about Anthony Nolan in a way that's fun and personal to Hollie.
"We can't believe how much support we have already had for this campaign.
"We are keen to find a donor while Hollie remains quite stable; we do not want it to get to a stage where she is very ill again which will make the procedure more difficult.
"Obviously we're desperate to find a donor for Hollie but this is not just for her - we realise the impact this can have for other families in the same situation. Even one extra donor signing up could transform someone's life."
Karen Archer, regional register development manager at Anthony Nolan, said: "The 'pants on your head selfie' idea has really taken off and is making a big difference in terms of the numbers joining the register.
"It's a great idea that's so personal to team Help Hollie whilst being a fun, interactive way of showing your support for our life-saving work. It's wonderful that such a simple concept could help save lives by raising awareness of the Anthony Nolan register.
"The support of sports people like Sam Warburton is particularly invaluable in helping us reach young men, which is really important as they are most likely to be chosen to donate but only represent 14% of the register."
:: Anyone aged 16 to 30 can sign up to the register. To find out more visit: www.anthonynolan.org/helphollie.