Beyonce will be performing for a good cause on Saturday June 1 at Twickenham Stadium in London, but her Sound of Change concert has taken a bit of a sinister turn. Queen Bey has been forced to beef up security due to a fan who is sending the pop diva threatening letters. Yikes!

All concert staff has been told to be on the lookout for Bassey Essien, the alleged letter-writer, who accused Beyonce of being an imposter -- so you know this guy has got some issues.

A source told The Sun, "Staff have been briefed on the situation and pictures of him have been passed round. They've been told to keep their eyes open and be extra vigilant," they continued, "Security has been increased on a few engagements now, especially for her U.K. promo. It is believed similar letters to the ones that Essien sent have been received."

Perhaps Bey was also spooked by the fan who got a little too friendly and smacked her butt at her concert in Copenhagen, Denmark. That would be enough to skeeve anyone out!

Bey's Sound of Change concert is boasting a majorly awesome lineup with Jennifer Lopez, Florence + the Machine, Ellie Goulding, Rita Ora and more set to perform. The concert will be all about girl power as Bey described the concert (via Billboard) as a "call for change for girls and women in the loudest voice possible. I am excited for us to come together on June 1 to bring the issues of education, health and justice for girls and women to the world stage."

We hope the concert goes off without a hitch and no trouble from Bey's stalker!