In libel/slander cases it's the responsibility of the accusing party to prove what they wrote/said is true. The accused party doesn't have to prove anything.
That depends on the country, and UK law is very unusual in it's placing the burden of proof on the defendant. Given Tebas is in Spain, talking in Spain to a Spanish newspaper, you're probably going to have to try and get him under Spanish law and IIRC last time this came up people worked out it's almost impossible to successfully sue someone for libel or defamation in Spain.