This is what we found on Wikipedia regarding the Kensington Palace: Entry Ticket:

Kensington (Olympia) is an interchange station between the Mildmay line of the London Overground and National Rail services operated by Southern, located in Kensington, West London. Limited services on the District line of the London Underground also operate to here.

The station is located in London fare zone 2. On the London Underground, it is the terminus of a short District line branch from Earl's Court, originally built as part of the Middle Circle. On the main-line railway it is on the West London line from Clapham Junction to Willesden Junction, by which trains bypass inner London. The station's name is drawn from its location in Kensington and the adjacent Olympia exhibition centre in West Kensington.

The station was originally opened in 1844 by the West London Railway but closed shortly afterwards. It reopened in 1862 and began catering for Great Western services the following year. In 1872 it became part of the Middle Circle train route that bypassed central London. The station was bombed during World War II and subsequently closed. It reopened in 1946 but the limited service to Clapham Junction was recommended for withdrawal in the 1960s Beeching Report. The main-line station was revitalised later in the decade as a terminus for national Motorail, and upgraded again in 1986 to serve a wider range of InterCity destinations. The station's Underground connection after World War II was limited to a shuttle service to and from Earl's Court.