Background: Sir Richard Starkey  (born 7 July 1940), known professionally as Ringo Starr, is an English musician, songwriter, singer, and actor who gained worldwide fame as the drummer for the Beatles. He occasionally sang lead vocals, usually for one song on an album, including "With a Little Help from My Friends", "Yellow Submarine", "Good Night", and their cover of "Act Naturally". He also wrote the Beatles' songs "Don't Pass Me By" and "Octopus's Garden", and is credited as a co-writer of others, including "What Goes On" and "Flying". Starr was twice afflicted by life-threatening illnesses during childhood, and he fell behind in school as a result of prolonged hospitalisations.
Context: When Starr married Maureen Cox in 1965, Beatles manager Brian Epstein served as best man, with Starr's stepfather Harry Graves and fellow Beatle George Harrison as witnesses. Soon afterwards, the couple's matrimony became the subject of a US novelty song, "Treat Him Tender, Maureen", by the Chicklettes. Starr and Maureen had three children together: Zak (born 13 September 1965), Jason (born 19 August 1967) and Lee (born 11 November 1970). In 1971, Starr purchased Lennon's former home, Tittenhurst Park at Sunninghill in Berkshire and moved his family there. Following Starr's repeated infidelities, the couple divorced in 1975. Maureen died from leukaemia at age 48 in 1994.  In 1980, while on the set of the film Caveman, Starr met actress Barbara Bach; they were married on 27 April 1981. In 1985, he was the first of the Beatles to become a grandfather upon the birth of Zak's daughter, Tatia Jayne Starkey. Zak Starkey is also a drummer, and during his father's regular absences, he spent time with The Who's Keith Moon. Zak has performed with his father during some All-Starr Band tours. In total, Ringo Starr has eight grandchildren - one from Zak, four from Jason and three from Lee. In 2016, he was the first Beatle to become a great-grandfather.  Starr and Bach split their time between homes in Cranleigh, Surrey; Los Angeles; and Monte Carlo. In the Sunday Times Rich List 2011, Starr was listed at number 56 in the UK with an estimated personal wealth of PS150 million. In 2012, Starr was estimated to be the wealthiest drummer in the world. In 2014 Starr announced that his 200-acre Surrey estate at Rydinghurst, with its Grade II-listed Jacobean house, was for sale. However, he retains a property in the London district of Chelsea off King's Road, and he and Bach continue to divide their time between London and Los Angeles.  In December 2015, Starr and Bach auctioned some of their personal and professional items to the public via Julien's Auctions in Los Angeles. Highlights of the collection included Starr's first Ludwig Black Oyster Pearl drum kit; instruments given to him by Harrison, Lennon and Marc Bolan; and a first-pressing copy of the Beatles' White Album numbered "0000001". The auction raised over $9 million, a portion of which was set aside for the Lotus Foundation, a charity founded by Starr and Bach.  In 2016, Starr expressed his support for the United Kingdom's withdrawal from the European Union, explaining: "I thought the European Union was a great idea, but I didn't see it going anywhere lately." In 2017 he described his impatience for Britain to "get on with" Brexit, declaring that "to be in control of your country is a good move."
Question: How many grandkids does he have?

Answer:
In total, Ringo Starr has eight grandchildren