Ivy Beattie Gestie Johnson

My gr-gn-father, Ivy Beattie Gestie Johnson (1861?-1917) was named by his father, Dr Thomas Revel Johnson 1818-1863 (aka Thomas Revel Guest II according to TRG's 1835 will), after Thomas's first cousin, Sir Ivor Bertie Guest (aka Lord Wymborne). Ivy's marriage and death certificates along with all newspaper articles and business dealings have him listed as Ivy however his wife Isabella, listed his name on his plot at Rookwood Cemetery, Sydney, in 1917 as Ivy AKA Ivor. When and how did she find out his real name was Ivor? According to p129 in the book "Lady Charlotte" [Bertie, who was Dr Thomas aunt], he and his sister Sarah Johnson (aka Sarah Guest) were "shipped off to Australia" in 1840, 5 years after Thomas Revel Guest (1870-1835) died. This was no doubt to rid the Guest family of the 2 reputed (illegitimate though accepted by their father) Guest/Johnson offspring.