Star Wars actor John Boyega is also set to appear at Windsor Castle bash
Minogue claims reality TV star could "dilute her brand" if successful
Yazoo cover appears on 'Kylie Christmas' festive album
'Kylie Christmas' will also feature James Corden and a posthumous duet with Frank Sinatra
The singer will headline the Barclaycard British Summertime gig series on June 21
Singer calls time on both bodies during her 'Kiss Me Once' tour of Australia
Pair cover Donna Summer's 'I Feel Love' and new collaboration 'Right Here Right Now'
Singer adds that days of extravagant tours might be over
Grace Jones and Chic feat. Nile Rodgers will also appear at London gig on June 21
Australian singer appears in '20,000 Days On Earth'