thanks to Kay
Olivia did not join Cliff for this tour. However, Cliff has always been an absolute gent to Olivia, and he mentions duetting with Olivia on Suddenly and getting featured in her Hollywood Nights TV Special in what he had been up to in the runup to this tour.
Extract from the written part says
In February/March I toured South Africa[...] Frome South Africa I flew to Los Angeles, where I appeared in Olivia Newton-John's TV show Hollywood Nights. After that Olivia and I recorded "Suddenly" for her LP Xanadu. As you know I have always enjoyed signing with Olivia, and it was simply wonderful to meet up with her again.